NorthWestern Energy (Nasdaq: NWE) posts Q1 2026 results and advances Black Hills merger

Filing Impact

(Very High)

Filing Sentiment

(Neutral)

Form Type

8-K

Rhea-AI Filing Summary

NorthWestern Energy Group reported mixed first quarter 2026 results while advancing a major merger and growth projects. GAAP diluted EPS was $1.03 versus $1.25 a year ago as net income fell to $63.5 million from $76.9 million, driven by weaker retail volumes and higher operating, merger, Colstrip and depreciation costs.

Non-GAAP diluted EPS rose to $1.31 from $1.22, reflecting adjustments for unfavorable weather, merger costs, PCCAM changes and Avista Colstrip interests. Revenue increased to $497.6 million from $466.6 million, and utility margin grew to $352.0 million from $328.4 million, helped by Montana electric base rate increases and Puget Colstrip margins.

The company affirmed 2026 non-GAAP EPS guidance of $3.68–$3.83 per diluted share and long‑term EPS and rate base growth of 4%–6%, supported by a $3.2 billion 2026‑2030 capital plan and a record $683 million 2026 capital program. A quarterly dividend of $0.67 per share is payable June 30, 2026.

NorthWestern highlighted progress on its all‑stock merger of equals with Black Hills Corporation, including shareholder approvals, regulatory settlements in Montana, Nebraska and South Dakota, and expiration of the Hart‑Scott‑Rodino waiting period, with closing targeted in the second half of 2026. The company also detailed Colstrip acquisitions, South Dakota wildfire liability reforms, data center development agreements and a planned $300 million, 131 MW South Dakota gas plant, alongside a $150 million bond issuance at 5.51% to refinance $60 million of 2.80% bonds.

Insights

Results are operationally solid with EPS mix and merger, project, and regulatory updates balancing out.

NorthWestern’s quarter shows a $13.4 million drop in GAAP net income to $63.5 million, mainly from higher operating, merger and Colstrip costs and softer volumes. Yet non‑GAAP EPS improved to $1.31 as weather, PCCAM and merger costs were stripped out and Montana rate relief and Puget Colstrip margins aided utility margin.

Management reaffirmed $3.68–$3.83 2026 non‑GAAP EPS guidance and long‑term 4%–6% EPS and rate base growth from a 2024 base, anchored by a $3.2 billion five‑year capital plan. Liquidity of $230.9 million versus $630.0 million a year earlier and higher debt costs highlight balance‑sheet pressure, partially addressed by a planned $150.0 million bond at 5.51% and redemption of $60.0 million of 2.80% bonds.

The all‑stock merger with Black Hills has cleared shareholder votes and the Hart‑Scott‑Rodino waiting period, with constructive state settlements and key hearings set for Q2 2026. Large‑load data center agreements, South Dakota wildfire liability reform, Colstrip acquisitions and a planned 131 MW South Dakota gas plant outline potential future earnings drivers, though much still depends on regulatory approvals, realized load growth and power prices.

8-K Event Classification

10 items: 0.2, 0.3, 0.5, 2.02, 5.3, 5.8, 6.3, 7.01, 8.2, 9.01

10 items

Item 0.2 Item 0.2

Item 0.3 Item 0.3

Item 0.5 Item 0.5

Item 2.02 Results of Operations and Financial Condition Financial

Disclosure of earnings results, typically an earnings press release or preliminary financials.

Item 5.3 Item 5.3

Item 5.8 Item 5.8

Item 6.3 Item 6.3

Item 7.01 Regulation FD Disclosure Disclosure

Material non-public information disclosed under Regulation Fair Disclosure, often investor presentations or guidance.

Item 8.2 Item 8.2

Item 9.01 Financial Statements and Exhibits Exhibits

Financial statements, pro forma financial information, and exhibit attachments filed with this report.

Key Figures

Q1 2026 Revenue: $497.6 million Q1 2026 GAAP diluted EPS: $1.03 per share Q1 2026 non-GAAP diluted EPS: $1.31 per share +5 more

8 metrics

Q1 2026 Revenue $497.6 million Total revenues for the quarter ended March 31, 2026 vs $466.6 million in 2025

Q1 2026 GAAP diluted EPS $1.03 per share Down from $1.25 per diluted share in Q1 2025

Q1 2026 non-GAAP diluted EPS $1.31 per share Adjusted diluted non-GAAP EPS vs $1.22 in Q1 2025

Q1 2026 Net income $63.5 million GAAP net income vs $76.9 million in Q1 2025

Q1 2026 Utility Margin $352.0 million Non-GAAP utility margin vs $328.4 million in Q1 2025, up 7.2%

2026 EPS guidance $3.68–$3.83 per diluted share Affirmed 2026 non-GAAP earnings guidance range

Five-year capital plan $3.2 billion Planned capital investment for 2026–2030 period

Liquidity at March 31, 2026 $230.9 million Includes $5.9 million cash and $225.0 million credit facility availability, vs $630.0 million a year earlier

Key Terms

Utility Margin, PCCAM, Adjusted Non-GAAP Diluted EPS, Allowance for Funds Used During Construction (AFUDC), +2 more

6 terms

Utility Margin financial

"Consolidated utility margin for the three months ended March 31, 2026 was $352.0 million as compared with $328.4 million"

PCCAM financial

"Under the PCCAM, net supply costs higher or lower than the PCCAM base rate were allocated 90 percent to Montana customers and 10 percent to shareholders."

Adjusted Non-GAAP Diluted EPS financial

"Adjusted Non-GAAP Diluted EPS for the same periods are $1.31 and $1.22, respectively."

Adjusted non-GAAP diluted EPS is a per-share profit figure that shows a company’s earnings after removing certain one-time, unusual, or non-cash items and dividing by the diluted share count (which includes potential shares). Investors use it like a cleaned-up snapshot of operating profit — similar to judging a car’s fuel efficiency by excluding a one-off trip — to compare underlying performance across periods or companies without short-term noise.

Allowance for Funds Used During Construction (AFUDC) financial

"This increase was due to higher borrowings and interest rates partly offset by higher capitalization of Allowance for Funds Used During Construction (AFUDC)."

Allowance for funds used during construction (AFUDC) is an accounting method that adds the cost of financing a long-term project—typically interest and related carrying costs—into the value of the asset while it is being built, rather than treating those costs as immediate expenses. For investors, AFUDC matters because it boosts reported asset value and can raise reported earnings during construction, affecting profitability comparisons and future return expectations much like rolling mortgage interest into the purchase price of a house changes both the asset’s book value and the apparent cost of owning it.

Planning Reserve Margin (PRM) financial

"The Southwest Power Pool (SPP) has recently updated its resource accreditation and Planning Reserve Margin (PRM) requirements in response to growing reliability concerns."

Hart-Scott-Rodino Antitrust Improvements Act regulatory

"the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act expired, permitting consummation of the transaction."

A U.S. law that requires companies planning large mergers or acquisitions to notify federal antitrust authorities and wait for review before completing the deal. Think of it like applying for a building permit: regulators check whether the combined business would unfairly hurt competition and can clear the deal, impose changes, or seek to stop it, so the process affects transaction timing, cost, and whether expected benefits reach investors.

Earnings Snapshot

Revenue: $497.6 million · Guidance included

Q1 2026

Revenue $497.6 million $31.0 million increase vs Q1 2025

GAAP diluted EPS $1.03 $0.22 decrease vs $1.25 in Q1 2025

Adjusted non-GAAP diluted EPS $1.31 $0.09 increase vs $1.22 in Q1 2025

Net income $63.5 million $13.4 million decrease vs $76.9 million in Q1 2025

Guidance

Affirmed 2026 non-GAAP EPS guidance of $3.68–$3.83 per diluted share, assuming normal weather, PCCAM waiver approval, 14–18% effective tax rate, and about 61.7 million diluted shares.

Understanding 8-K Material Events →

04/30/2026 - 11:19 AM

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 OR 15(d) of The Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): April 29, 2026

NorthWestern Energy Group, Inc.

(Exact name of registrant as specified in its charter)

Delaware

000-56598

93-2020320

(State or other jurisdiction of
incorporation or organization)

(Commission File Number)

(I.R.S. Employer Identification No.)

3010 W. 69th Street

Sioux Falls

South Dakota

57108

(Address of principal executive offices)

(Zip Code)

Registrant’s telephone number, including area code: 605-978-2900

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:


Registrant	Title of each class	Trading Symbol(s)	Name of each exchange on which registered
NorthWestern Energy Group, Inc.	Common stock	NWE	Nasdaq Stock Market LLC

Indicate by check mark whether the registrant is an emerging growth company as defined in as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging Growth Company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.

☐

Item 2.02 Results of Operations and Financial Condition

On April 29, 2026, NorthWestern Energy Group, Inc. d/b/a NorthWestern Energy (Nasdaq: NWE) (the “Company”), issued a press release (the “Press Release”) discussing financial results for the quarter ended March 31, 2026, and affirming earnings guidance for 2026 in the range of $3.68 to $3.83 per diluted share. The Press Release is furnished as Exhibit 99.1 hereto and is incorporated herein by reference.

The information in this Current Report on Form 8-K provided under Item 2.02 shall not be deemed “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liabilities of that Section. The information provided under Item 2.02 in this Current Report shall not be incorporated by reference into any registration statement or other document pursuant to the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

Item 7.01 Regulation FD Disclosure.

Annual Meeting Presentation. As previously announced and as stated in the Press Release, on April 30, 2026, at 12:00 a.m. Eastern time (10:00 a.m. Mountain time), the Company will hold its virtual annual meeting of shareholders. A virtual annual meeting enables our shareholders—regardless of size, resources, or physical location—to participate in the annual meeting at no cost. We are committed to ensuring that shareholders will be afforded the same rights and opportunities to participate at our virtual meeting as they would in person.

The annual meeting will be webcast live on the internet and can be accessed by visiting www.virtualshareholdermeeting.com/NWE2026. To listen to the meeting, please go to the site at least 10 minutes in advance of the meeting and follow the check-in procedures.

During the annual meeting, Brian Bird, president and chief executive officer of the Company will make a presentation (the "Annual Meeting Presentation") to shareholders and other attendees that will discuss the Company's operations.

Earnings Call Presentation. As previously announced and as stated in the Press Release, the Company will host an investor conference call and webcast on April 30, 2026, at 3:30 p.m. Eastern time to review its financial results. During the conference call, Brian Bird, president and chief executive officer, and Crystal Lail, vice president and chief financial officer, will make a slide presentation (the "Investor Call Presentation") concerning the Company's financial results.

A live webcast of the investor conference call can be accessed from the Company’s website at www.northwesternenergy.com/earnings-registration. To listen and view the slideshow presentation, please go to the site at least 15 minutes in advance of the call to register. An archived webcast will be available shortly after the event and remain active for one year.

Copies of the Annual Meeting Presentation and the Investor Call Presentation are being furnished pursuant to Regulation FD as Exhibits 99.2 and 99.3, respectively, to this Current Report on Form 8-K and are incorporated herein by reference. The information in the presentations shall not be deemed to be “filed” for the purposes of Section 18 of the Securities Exchange Act of 1934, as amended, or otherwise subject to the liability of that section. Furthermore, the presentations shall not be deemed to be incorporated by reference into the Company's filings under the

Securities Act of 1933, as amended, or under the Securities Exchange Act of 1934, as amended, except as set forth with respect thereto in any such filing.

Item 9.01 Financial Statements and Exhibits.


Exhibit No.						Description of Document
99.1*						Press Release, dated April 29, 2026
99.2*						Annual Meeting Presentation, dated April 30, 2026
99.3*						Investor Call Presentation, dated April 30, 2026
104						Cover Page Interactive Data File – the cover page XBRL tags are embedded within the Inline XBRL document

* filed herewith

Signatures

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.


						NorthWestern Energy Group, Inc.

			By:			/s/ Timothy P. Olson
						Timothy P. Olson
						Corporate Secretary

Date: April 30, 2026


			NorthWestern Energy Group, Inc. d/b/a NorthWestern Energy 3010 W. 69th Street Sioux Falls, SD 57108 www.northwesternenergy.com

FOR IMMEDIATE RELEASE

NorthWestern Energy Reports First Quarter 2026 Financial Results

•First Quarter 2026 Diluted GAAP EPS of $1.03, compared to $1.25 in 2025.

•First Quarter 2026 Adjusted Diluted Non-GAAP EPS of $1.31, compared to $1.22 in 2025.

•Affirms 2026 earnings guidance range of $3.68 to $3.83 per diluted share.

•Affirms record $683 million capital plan for 2026 and 4% to 6% long-term EPS and rate base growth rate.

•Announces $0.67 per share quarterly dividend - payable June 30, 2026.

•Received shareholder approval of all merger proposals and reached constructive settlement agreements with certain key intervenors in Montana, Nebraska, and South Dakota.

BUTTE, MT / SIOUX FALLS, SD - April 29, 2026 - NorthWestern Energy Group, Inc. d/b/a NorthWestern Energy (Nasdaq: NWE) reported financial results for the First Quarter of 2026. Net income for the period was $63.5 million, or $1.03 per diluted share, as compared with net income of $76.9 million, or $1.25 per diluted share, for the same period in 2025. This decrease was primarily due to retail volumes, operating, administrative, and general costs, including merger-related costs and costs associated with our additional ownership interests in Colstrip Units 3 and 4, depreciation expense, and interest expense. These were offset in part by new rates, transmission revenues, and lower non-recoverable Montana electric supply costs.

NorthWestern’s First Quarter 2026 non-GAAP net income and diluted earnings per share were $80.6 million and $1.31, respectively, compared to $75.3 million and $1.22 in 2025. See “Adjusted Non-GAAP Earnings” and “Non-GAAP Financial Measures” sections below for more information on these measures.

“The first quarter included several important developments across our regulatory and strategic priorities,” said President and CEO Brian Bird. “In South Dakota, the signing of Senate Bill 36 into law provided greater clarity around wildfire‑related liabilities and strengthened our ability to manage risk associated with critical energy infrastructure, aligning South Dakota with similar wildfire liability protections enacted in Montana last year. In Montana, we also submitted our Large New Load tariff rule proposal to the Public Service Commission—an important step in protecting existing customers while supporting long‑term energy investment and economic development in the state. Additionally, earlier this week we executed a development agreement with Quantica Infrastructure to advance it’s Big Sky Digital Infrastructure campus outside of Billings, MT.

Bird continues, “We also made great progress on the merger. In March, we reached a constructive settlement agreement with the Public Advocate of Nebraska, followed by a hearing in early April. Also in April, both NorthWestern and Black Hills shareholders approved the merger proposals and we were able to reach constructive settlements with certain key intervenors in both Montana and South Dakota. Together, these milestones meaningfully advance us toward a targeted second‑half 2026 closing of the transaction."

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 2

TRANSACTION UPDATE

On August 18, 2025, we entered into a Merger Agreement with Black Hills Corporation and a wholly owned subsidiary of Black Hills. The Merger Agreement provides for an all-stock merger of equals between NorthWestern and Black Hills upon the terms and subject to the conditions set forth therein. The new corporate name selected for the resulting parent company of the combined corporate group is Bright Horizon Energy.

We have filed applications with the Montana Public Service Commission (MPSC), Nebraska Public Service Commission (NPSC), South Dakota Public Utilities Commission (SDPUC), and Federal Energy Regulatory Commission (FERC) for approval of the Merger.

In March 2026, we reached a settlement agreement with the Public Advocate of Nebraska, which is subject to approval by the NPSC. A hearing with the NPSC was held in April 2026.

In April 2026, shareholders of each company voted to approve the Merger and the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act expired, permitting consummation of the transaction.

In April 2026, we reached settlement agreements with certain key intervenors in both Montana and South Dakota, which are subject to approval by the MPSC and SDPUC, respectively. Hearings with the MPSC and SDPUC are scheduled in the second quarter of 2026.

We anticipate the transaction closing in the second half of 2026, subject to the satisfaction or waiver of certain closing conditions.

During the three months ended March 31, 2026, we have incurred $3.4 million of merger-related costs, which are included in our Administrative and general expenses.

FINANCIAL OUTLOOK

Affirming 2026 Guidance and Long-Term Growth Rates

We are affirming our 2026 non-GAAP earnings guidance of $3.68 - $3.83 per diluted share. This guidance is based upon, but not limited to, the following major assumptions:

•Normal weather in our service territories;

•Excludes costs related to the pending merger with Black Hills Corp.;

•Approval of the Power Cost and Credit Adjustment Mechanism (PCCAM) waiver and power prices sufficient to recover operating expense from incremental Avista and Puget Colstrip interests;

•An effective income tax rate of approximately 14 percent to 18 percent; and

•Diluted average shares outstanding of approximately 61.7 million.

We are affirming our long-term diluted earnings per share growth guidance of 4% to 6%, based on our 2024 adjusted diluted non-GAAP EPS baseline of $3.40.

Additionally, we are affirming our $3.2 billion capital investment plan for 2026-2030, which is expected to support rate base growth of 4% to 6% from our 2024 base year of approximately $5.4 billion.

We anticipate funding capital expenditures through cash flows from operations, available credit sources, debt issuances, and future rate increases. In order to fund South Dakota generation investment, equity issuances are expected beginning in 2027.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 3

Dividend Declared

NorthWestern Energy Group’s Board of Directors has declared a quarterly common stock dividend of $0.67 per share payable on June 30, 2026, to shareholders of record as of June 15, 2026.

Looking ahead, we remain committed to maintaining a dividend payout ratio within our targeted range of 60-70% over the long term.

Additional information regarding this release can be found in the earnings presentation at
https://www.northwesternenergy.com/investors/earnings.

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NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 4

COMPANY UPDATES

Montana Rate Review

In December 2025, the MPSC issued a final order approving our partial electric settlement agreement. The final order also suspended the 90/10 cost sharing mechanism of the PCCAM on a temporary basis pending further review by the MPSC. Within this final order, the MPSC disallowed a portion of the capital costs related to the construction of Yellowstone County Generating Station (YCGS). As a result, in the fourth quarter of 2025 we recorded a $30.9 million non-cash charge for the regulatory disallowance.

In January 2026, we filed a Motion for Reconsideration (Motion) as it relates to this final order. Among other things, our Motion requests that the MPSC reconsider their prudence conclusions regarding the capital costs associated with the construction of YCGS and clarification as to the effective date of the PCCAM sharing mechanism suspension, for which we have requested an effective date of July 1, 2025, to align with the PCCAM tracker year. Any subsequent modifications by the MPSC to their final order will be reflected in our 2026 results.

Montana Large New Load Tariff Rule

In March 2026, we filed an application with the MPSC requesting approval of a Large New Load tariff rule (LNL Rule) to establish requirements and contract terms for providing electric service to bundled customers with new or expanded loads of five megawatts or greater, including data centers and other energy-intensive operations. This filing establishes a framework governing agreements between us and large new load customers and is intended to address the costs and operational considerations associated with serving those loads while protecting existing customers from cost shifting and other adverse impacts. Under this proposed framework, for the largest commitments, 50 megawatts or greater, we would file the executed Electric Service Agreement with the MPSC for review and approval before service begins. For customers with loads between 5 and 49 megawatts, the tariff's standardized process and mandatory protections apply, but individual agreements do not require case-specific MPSC approval filings. This application initiates a public regulatory proceeding that will include opportunities for review and public comment consistent with MPSC procedures.

Data Center Development

As previously disclosed, we have signed development agreements with both Sabey Data Centers and Atlas Power Holdings LLC to provide electric supply services for data centers being developed in Montana. In April 2026, we signed a development agreement with Quantica Infrastructure to evaluate the transmission infrastructure and generation resources needed to support their proposed need. The combined energy service requirement associated with these development agreements is currently expected to be 150 megawatts beginning in late 2027, with growth of up to approximately 1,500 megawatts or more by 2030. We are working with each of these parties to execute electric service agreements.

Resources and regulatory mechanisms, such as the LNL Rule discussed above, to be utilized for serving these requests are pending further evaluation and regulatory considerations.

Colstrip Acquisitions and Requests for Cost Recovery

As previously disclosed, we entered into definitive agreements with Avista and Puget to acquire their respective interests in Colstrip Units 3 and 4 for $0 and completed these acquisitions on January 1, 2026. Accordingly, we are responsible for the associated operating costs beginning on January 1, 2026, which we will not collect through utility base rates until requested in a future Montana rate review. Puget and Avista will remain responsible for their respective pre-closing share of environmental, asset retirement obligations, and pension liabilities attributed to events or conditions existing prior to the closing of the transaction and for any future decommissioning and demolition costs associated with the existing facilities that comprise their interests.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 5

Avista Interests - The 222 megawatts of generation capacity from Colstrip Units 3 and 4 acquired from Avista (Avista Interests) on January 1, 2026, was identified as a key element in our strategy to achieve resource adequacy for customers, as outlined in our 2023 Montana Integrated Resource Plan. Noting the costs associated with operating this resource are not currently reflected in utility customer rates, in August 2025, we filed a temporary PCCAM tariff waiver request with the MPSC that could provide a near-term cost-recovery mechanism to offset a portion of the approximately $18.0 million in annual incremental operating and maintenance costs associated with the Avista Interests. This waiver requested that the MPSC allow us to keep 100 percent of the net revenue associated with certain designated power sales contracts up to the amount of the operating and maintenance expenses we incur associated with our Avista Interests. Furthermore, the waiver request indicated that any net revenues from the designated contracts exceeding the operating and maintenance expenses associated with our Avista Interests would continue to flow back to retail customers. In January 2026, the MPSC approved our PCCAM tariff waiver request on an interim basis with final approval or denial subject to the ongoing PCCAM docket process.

During the three months ended March 31, 2026, power prices in the Pacific Northwest associated with these designated power sales contracts included within our PCCAM tariff waiver were insufficient to contribute to the recovery of the operating and maintenance expenses associated with the Avista Interests.

Puget Interests - The 370 megawatts of generation capacity from Colstrip Units 3 and 4 acquired from Puget (Puget Interests) on January 1, 2026, increases our ownership share of the facility to 55 percent and provides an increase in voting share in determining strategic direction and investment decisions at the facility. Unlike the Avista Interests, we do not currently need this capacity to serve existing customers in Montana. As such, the Puget Interests are held by our FERC regulated subsidiary to isolate the costs associated with this acquired interest from our Montana retail customers. While we expect our future opportunity to serve growing customer demand, including large-load customers, may be supported by this resource, in October 2025, we signed a contract to sell the dispatchable capacity and associated energy from the Puget Interests beginning January 1, 2026, through late 2027. Revenues from this agreement are expected to largely offset the estimated $30.0 million of annual incremental operating and maintenance costs associated with the Puget Interests. In addition, in October 2025, we submitted a request to the FERC for approval of cost-based rates for our subsidiary that will own the Puget Interests. In February 2026, the FERC approved both the cost-based rates and the contract rates retroactive to January 1, 2026. In March 2026, two MPSC commissioners, in their individual capacity, filed a motion with the FERC requesting a rehearing that largely reiterated arguments previously rejected by the FERC. We anticipate that the FERC will rule on this motion in the second quarter of 2026. If the FERC denies the motion, its order will stand. If the FERC grants the motion, it could reopen all or some portion of the proceedings.

Generation Capacity in South Dakota

The Southwest Power Pool (SPP) has recently updated its resource accreditation and Planning Reserve Margin (PRM) requirements in response to growing reliability concerns. As a result, SPP is requiring additional accredited capacity by 2030 to meet the updated PRM targets. In October 2025, we submitted a project with the SPP under their Expedited Resource Adequacy Study program for the construction of a 131 MW natural gas generating facility located in Aberdeen, South Dakota, to meet regional capacity needs by 2030. Anticipated costs for this project are approximately $300.0 million.

Regional Transmission Development Activities

In December 2024, we signed a nonbinding memorandum of understanding (MOU) with North Plains Connector LLC, a wholly owned subsidiary of Grid United, to own 10 percent (300 megawatts) of the North Plains Connector (NPC) Consortium project. The project is entering the permitting phase. Currently, construction is planned to commence in 2028, subject to receipt of regulatory approvals, with the project expected to be operational by 2032. Under the terms of the MOU, Grid United will continue to fund the development of the NPC and we will make our investment decision when the regulatory approvals and permits are in place. The project is a critical infrastructure investment that aligns with our commitment to providing reliable and affordable energy to our customers while also supporting broader grid resilience efforts in the region.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 6

We have also entered into a nonbinding letter of intent with Grid United to continue transmission development to further enhance the grid through the southwest corridor of Montana. Development to expand the southwest corridor of Montana through grid build out would represent a significant step in enhancing connectivity between Montana and the broader Western energy market - bolstering grid reliability, allowing for critical import capability, and enabling customers to access and benefit from emerging energy markets in the West.

South Dakota Wildfire Risk Mitigation

The South Dakota Legislature approved Senate Bill 36, and the Governor signed this bill into law, in March 2026. It precludes common law strict liability claims for utility operations alleged to have caused wildfire-related damages; establishes a statutory standard of care, supplanting common law causes of action and other theories of recovery; and creates a rebuttable presumption that a valid and current wildfire mitigation plan is reasonable preparation for, and mitigation of, wildfire risk. The legislation also defines the availability of damages by allowing noneconomic personal injury damages only when there is bodily injury and punitive damages only when an injured party proves by clear and convincing evidence that a qualified utility acted with willful and wanton misconduct and the qualified utility's willful and wanton misconduct was the actual and proximate cause of damages to the plaintiff. We anticipate filing our wildfire mitigation plan with the SDPUC in the second half of 2026.

Financing Update

On April 28, 2026, NWE Public Service priced $150.0 million aggregate principal amount of South Dakota First Mortgage Bonds at a fixed interest rate of 5.51 percent maturing on June 15, 2036. We expect to complete the issuance and sale of these bonds on June 15, 2026. A portion of the proceeds will be utilized to redeem all $60.0 million of NWE Public Service's 2.80 percent South Dakota First Mortgage Bonds due on June 15, 2026.

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NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 7

CONSOLIDATED STATEMENT OF INCOME


	Three Months Ended March 31,
($ in millions, except per share amounts)	2026		2025
Revenues
Electric	$	362.1	$	335.5
Gas	135.5		131.1
Total Revenues	497.6		466.6
Operating expenses
Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	145.6		138.2
Operating and maintenance	74.5		56.7
Administrative and general	46.1		41.4
Property and other taxes	50.4		43.2
Depreciation and depletion	66.8		62.4
Total Operating Expenses	383.5		341.9
Operating income	114.1		124.7
Interest expense, net	(39.9)		(36.5)
Other income, net	3.1		3.9
Income before income taxes	77.3		92.1
Income tax expense	(13.8)		(15.2)
Net Income	$	63.5	$	76.9

Average Common Shares Outstanding	61.5		61.3
Basic Earnings per Average Common Share	$	1.03	$	1.25
Diluted Earnings per Average Common Share	$	1.03	$	1.25

Dividends Declared per Common Share	$	0.67	$	0.66
Note: Subtotal variances may exist due to rounding.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

Page 8

RECONCILIATION OF PRIMARY CHANGES DURING THE QUARTER


	Three Months Ended March 31, 2026 vs. 2025
($ in millions, except per share amounts)	Pre-tax Income		Income Tax (Expense) Benefit (3)		Net Income		Diluted Earnings Per Share

First Quarter, 2025	$	92.1	$	(15.2)	$	76.9	$	1.25
Variance in revenue and fuel, purchased supply, and direct transmission expense(1) items impacting net income:
Rates	23.7		(6.0)		17.7		0.29
Electric margin from the acquisition of the Colstrip Puget Interests	5.5		(1.4)		4.1		0.07
Production tax credits, offset within income tax expense	2.6		(2.6)		—		—
Electric transmission revenue	2.2		(0.6)		1.6		0.02
Non-recoverable Montana electric supply costs	2.0		(0.5)		1.5		0.02
Electric retail volumes	(12.2)		3.1		(9.1)		(0.15)
Natural gas retail volumes	(6.2)		1.6		(4.6)		(0.08)
Montana property tax tracker collections	(3.3)		0.8		(2.5)		(0.04)
Natural gas production step down	(0.7)		0.2		(0.5)		(0.01)
Other	4.0		(1.0)		3.0		0.05

Variance in expense items(2) impacting net income:
Operating, maintenance, and administrative, excluding merger-related costs	(20.0)		5.1		(14.9)		(0.24)
Depreciation	(4.4)		1.1		(3.3)		(0.05)
Interest expense	(3.4)		0.9		(2.5)		(0.04)
Property and other taxes not recoverable within trackers	(2.0)		0.5		(1.5)		(0.02)
Merger-related costs	(3.4)		0.5		(2.9)		(0.05)
Other	0.8		(0.3)		0.5		0.01
Dilution from higher share count							—
First Quarter, 2026	$	77.3	$	(13.8)	$	63.5	$	1.03
Change in Net Income					$	(13.4)	$	(0.22)
(1) Exclusive of depreciation and depletion shown separately below (2) Excluding fuel, purchased supply, and direct transmission expense (3) Income Tax (Expense) Benefit calculation on reconciling items assumes blended federal plus state effective tax rate of 25.3%.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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EXPLANATION OF CONSOLIDATED RESULTS

Three Months Ended March 31, 2026 Compared with the Three Months Ended March 31, 2025

Consolidated gross margin for the three months ended March 31, 2026 was $160.3 million as compared with $166.2 million in 2025, a decrease of $5.9 million, or 3.5 percent. This decrease was primarily due to retail volumes, operating expenses, including costs associated with our additional ownership interests in Colstrip Units 3 and 4, and depreciation expense. These were offset in part by new rates, transmission revenues, and lower non-recoverable Montana electric supply costs.


($ in millions)	Three Months Ended March 31,
Reconciliation of gross margin to utility margin:	2026		2025

Operating Revenues	$	497.6	$	466.6
Less: Fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion shown separately below)	145.6		138.2
Less: Operating and maintenance	74.5		56.7
Less: Property and other taxes	50.4		43.1
Less: Depreciation and depletion	66.8		62.4
Gross Margin	160.3		166.2

Add back: Operating and maintenance	74.5		56.7
Add back: Property and other taxes	50.4		43.1
Add back: Depreciation and depletion	66.8		62.4
Utility Margin(1)	$	352.0	$	328.4
(1) Non-GAAP financial measure. See “Non-GAAP Financial Measures” below.


	Three Months Ended March 31,
($ in millions)	2026		2025		Change		% Change
Utility Margin
Electric	$	271.8	$	242.7	$	29.1	12.0	%
Natural Gas	80.2		85.7		(5.5)		(6.4)
Total Utility Margin(1)	$	352.0	$	328.4	$	23.6	7.2	%
(1) Non-GAAP financial measure. See “Non-GAAP Financial Measures” below.

Consolidated utility margin for the three months ended March 31, 2026 was $352.0 million as compared with $328.4 million for the same period in 2025, an increase of $23.6 million, or 7.2 percent.

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Primary components of the change in utility margin include the following:


($ in millions)	Utility Margin 2026 vs. 2025
Utility Margin Items Impacting Net Income
Base rates	$	23.7
Electric margin from the acquisition of the Puget Interests	5.5
Transmission revenue due to market conditions and rates	2.2
Non-recoverable Montana electric supply costs	2.0
Electric retail volumes	(12.2)
Natural gas retail volumes (including a $3.2 million increase due to acquisition of Energy West Operations)	(6.2)
Montana property tax tracker collections	(3.3)
Natural gas production step down	(0.7)
Other	4.0
Change in Utility Margin Items Impacting Net Income	15.0
Utility Margin Items Offset Within Net Income
Property and other taxes recovered in revenue, offset in property and other taxes	5.2
Production tax credits, offset in income tax expense	2.6
Operating expenses recovered in revenue, offset in operating and maintenance expense	0.8
Change in Utility Margin Items Offset Within Net Income	8.6
Increase in Consolidated Utility Margin(1)	$	23.6
(1) Non-GAAP financial measure. See “Non-GAAP Financial Measures” below.

Electric retail volumes were driven by unfavorable weather partly offset by customer growth. Natural gas retail volumes were driven by unfavorable weather partly offset by customer growth and the acquisition of Energy West operations.

Under the PCCAM, net supply costs higher or lower than the PCCAM base rate (PCCAM Base) (excluding qualifying facility costs) were allocated 90 percent to Montana customers and 10 percent to shareholders. Effective February 1, 2026 the cost sharing mechanism of the PCCAM was suspended on a temporary basis pending further review by the MPSC. For the three months ended March 31, 2026, we under-collected supply costs of $20.7 million resulting in an increase to our under collection of costs, and recorded a decrease in pre-tax earnings of $0.7 million (10 percent of the PCCAM Base cost variance for January 2026). For the three months ended March 31, 2025, we under-collected supply costs of $24.3 million resulting in an increase to our under collection of costs, and recorded a decrease in pre-tax earnings of $2.7 million (10 percent of the PCCAM Base cost variance).

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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	Three Months Ended March 31,
($ in millions)	2026		2025		Change		% Change
Operating Expenses (excluding fuel, purchased supply and direct transmission expense)
Operating and maintenance	$	74.5	$	56.7	$	17.8	31.4	%
Administrative and general	46.1		41.4		4.7		11.4
Property and other taxes	50.4		43.2		7.2		16.7
Depreciation and depletion	66.8		62.4		4.4		7.1
Total Operating Expenses (excluding fuel, purchased supply and direct transmission expense)	$	237.8	$	203.7	$	34.1	16.7	%

Consolidated operating expenses, excluding fuel, purchased supply and direct transmission expense, were $237.8 million for the three months ended March 31, 2026, as compared with $203.7 million for the three months ended March 31, 2025. Primary components of the change include the following:


	Operating Expenses
($ in millions)	2026 vs. 2025
Operating Expenses (excluding fuel, purchased supply and direct transmission expense) Impacting Net Income
Electric generation maintenance (Including $6.4 million and $3.9 million due to the acquisition of the Puget Interests and Avista Interests, respectively)	$	10.1
Depreciation expense due to plant additions and higher depreciation rates	4.4
Labor and benefits(1)	3.5
Merger-related costs, including consulting and legal fees	3.4
Property and other taxes not recoverable within trackers	2.0
Wildfire mitigation expense, partly offset by higher base revenues	1.9
Insurance expense, primarily due to increased wildfire risk premiums	0.7
Uncollectible accounts	0.5
Technology implementation and maintenance expenses	0.2
Other	3.1
Change in Items Impacting Net Income	29.8

Operating Expenses Offset Within Net Income
Property and other taxes recovered in trackers, offset in revenue	5.2
Operating and maintenance expenses recovered in trackers, offset in revenue	0.8
Pension and other postretirement benefits, offset in other income(1)	(0.7)
Deferred compensation, offset in other income	(1.0)
Change in Items Offset Within Net Income	4.3
Increase in Operating Expenses (excluding fuel, purchased supply and direct transmission expense)	$	34.1
(1) In order to present the total change in labor and benefits, we have included the change in the non-service cost component of our pension and other postretirement benefits, which is recorded within other income on our Condensed Consolidated Statements of Income. This change is offset within this table as it does not affect our operating expenses.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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We estimate property taxes throughout each year, and update those estimates based on valuation reports received from the Montana Department of Revenue. Under Montana law, we are allowed to track the increases and decreases in the actual level of state and local taxes and fees and adjust our rates to recover the increase or decrease between rate cases less the amount allocated to FERC-jurisdictional customers and net of the associated income tax benefit.

Consolidated operating income for the three months ended March 31, 2026 was $114.1 million as compared with $124.7 million in the same period of 2025. This decrease was primarily due to retail volumes, operating, administrative, and general costs, including merger-related costs and costs associated with our additional ownership interests in Colstrip Units 3 and 4, and depreciation expense. These were offset in part by new rates, transmission revenues, and lower non-recoverable Montana electric supply costs.

Consolidated interest expense was $39.9 million for the three months ended March 31, 2026 as compared with $36.5 million for the same period of 2025. This increase was due to higher borrowings and interest rates partly offset by higher capitalization of Allowance for Funds Used During Construction (AFUDC).

Consolidated other income was $3.1 million for the three months ended March 31, 2026 as compared with $3.9 million for the same period of 2025. This decrease was primarily due to higher non-service component pension expense and a decrease in the value of deferred shares held in trust for deferred compensation partly offset by higher capitalization of AFUDC.

Consolidated income tax expense was $13.8 million for the three months ended March 31, 2026 as compared to $15.2 million for the same period of 2025. Our effective tax rate for the three months ended March 31, 2026 was 17.9% as compared with 16.5% for the same period in 2025.

The following table summarizes the differences between our effective tax rate and the federal statutory rate:


	Three Months Ended March 31,
($ in millions)	2026				2025
	(in dollars)		(in percent)		(in dollars)		(in percent)
Income before income taxes	$	77.3			$	92.1

Income tax calculated at federal statutory rate	16.2		21.0	%	19.4		21.0	%

State income tax, net of federal provision	1.1		1.4		0.9		0.9
Tax Credits
Production tax credits	(0.5)		(0.6)		(2.1)		(2.3)
Other	—		—		0.5		0.5
Impact of utility ratemaking on income taxes
Flow-through repairs deductions	(7.6)		(9.8)		(8.0)		(8.7)
Amortization of excess deferred income taxes	(1.3)		(1.7)		(0.7)		(0.7)
AFUDC, net	(0.6)		(0.8)		(0.7)		(0.8)
Plant and depreciation of flow through items	6.3		8.2		5.3		5.8
Changes in Unrecognized Tax Benefits
Interest and penalties	—		—		0.3		0.3
Nontaxable and nondeductible items	0.2		0.2		0.3		0.5
	(2.4)		(3.1)		(4.2)		(4.5)

Income Tax Expense and Effective Tax Rate	$	13.8	17.9	%	$	15.2	16.5	%

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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We compute income tax expense for each quarter based on the estimated annual effective tax rate for the year, adjusted for certain discrete items. Our effective tax rate typically differs from the federal statutory tax rate primarily due to the regulatory impact of flowing through federal and state tax benefits of repairs deductions, state tax benefit of accelerated tax depreciation deductions (including bonus depreciation when applicable) and production tax credits.

LIQUIDITY AND OTHER CONSIDERATIONS

Liquidity and Capital Resources

As of March 31, 2026, our total net liquidity was approximately $230.9 million, including $5.9 million of cash and cash equivalents and $225.0 million of revolving credit facility availability with no letters of credit outstanding. This compares to total net liquidity one year ago at March 31, 2025 of $630.0 million.

Earnings Per Share

Basic earnings per share are computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding for the period. Diluted earnings per share reflect the potential dilution of common stock equivalent shares that could occur if unvested shares were to vest. Common stock equivalent shares are calculated using the treasury stock method, as applicable. The dilutive effect is computed by dividing earnings applicable to common stock by the weighted average number of common shares outstanding plus the effect of the outstanding unvested restricted stock and performance share awards. Average shares used in computing the basic and diluted earnings per share are as follows:


	Three Months Ended
	March 31, 2026	March 31, 2025
Basic computation	61,460,756	61,339,498
Dilutive effect of:
Performance and restricted share awards(1)	171,246	86,603
Diluted computation	61,632,002	61,426,101
(1) Performance share awards are included in diluted weighted average number of shares outstanding based upon what would be issued if the end of the most recent reporting period was the end of the term of the award.

As of March 31, 2026, there were no shares from performance and restricted share awards which were antidilutive and excluded from the earnings per share calculations, compared to 49,071 shares as of March 31, 2025.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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Adjusted Non-GAAP Earnings

We reported GAAP earnings of $1.03 per diluted share for the three months ended March 31, 2026 and $1.25 per diluted share for the same period in 2025. Adjusted Non-GAAP earnings per diluted share for the same periods are $1.31 and $1.22, respectively. A reconciliation of items factored into our Adjusted Non-GAAP diluted earnings are summarized below. The amount below represents a non-GAAP measure that may provide users of this data with additional meaningful information regarding the impact of certain items on our expected earnings. More information on this measure can be found in the "Non-GAAP Financial Measures" section below.


($ in millions, except EPS)

Three Months Ended March 31, 2026
	Pre-tax Income	Net(1) Income	Diluted EPS
2026 Reported GAAP	$77.3	$63.5	$1.03

Non-GAAP Adjustments:
Add Back Unfavorable Weather	14.4	10.8	0.17
Merger-Related Costs(2)	3.4	2.9	0.05
Remove January PCCAM Expense Following MPSC Suspension of 90/10 Sharing	0.7	0.5	0.01
Colstrip Avista Interests(3)	3.9	2.9	0.05
2026 Adj. Non-GAAP	$99.7	$80.6	$1.31


Three Months Ended March 31, 2025
	Pre-tax Income	Net(1) Income	Diluted EPS
2025 Reported GAAP	$92.1	$76.9	$1.25

Non-GAAP Adjustments:
Deduct Favorable Weather	(2.2)	(1.6)	(0.03)

2025 Adj. Non-GAAP	$89.9	$75.3	$1.22

(1) Income tax rate on reconciling items assumes blended federal plus state effective tax rate of 25.3%. (2) Certain merger-related costs are not tax-deductible. (3) Power prices in the Pacific Northwest associated with the designated power sales contracts included within our temporary PCCAM tariff waiver were insufficient to recover the operating expenses associated with the Avista Interests.

NorthWestern Energy Reports First Quarter 2026 Financial Results

April 29, 2026

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Company Hosting Earnings Webinar

NorthWestern will host an investor earnings webinar on Thursday, April 30, 2026, at 3:30 p.m. Eastern time to review its financial results for the three months ended March 31, 2026. To register for the webinar, please visit www.northwesternenergy.com/earnings-registration. Please go to the site at least 15 minutes in advance of the webinar to register. An archived webinar will be available shortly after the event and remain active for one year.

Notice of Virtual Annual Shareholders Meeting

The virtual Annual Shareholders Meeting will be held on Thursday, April 30, 2026, at 12:00 p.m. Eastern. A virtual Annual Meeting enables our shareholders — regardless of size of investment, resources, or physical location — to participate in the meeting at no cost. We are committed to ensuring that shareholders will be afforded the same rights and opportunities to participate at our virtual meeting as they would in person.

The Annual Meeting will be webcast live and can be accessed by visiting

http://www.virtualshareholdermeeting.com/NWE2026. To participate in the meeting, please go to the site at least 15 minutes in advance of the meeting and follow the check-in procedures.

NorthWestern Energy - Delivering a Bright Future

NorthWestern Energy Group, doing business as NorthWestern Energy, provides essential energy infrastructure and valuable services that enrich lives and empower communities while serving as long-term partners to our customers and communities. We work to deliver safe, reliable, and innovative energy solutions that create value for customers, communities, employees, and investors. We do this by providing low-cost and reliable service performed by highly-adaptable and skilled employees. We provide electricity and / or natural gas to approximately 850,300 customers in Montana, South Dakota, Nebraska, and Yellowstone National Park. Upon the completion of the holding company reorganization in 2023, NW Corp became a subsidiary of NorthWestern Energy Group. Our operations in Montana and Yellowstone National Park are conducted through our subsidiary, NW Corp, and our operations in South Dakota and Nebraska are conducted through our subsidiary, NWE Public Service. We have provided service in South Dakota and Nebraska since 1923 and in Montana since 2002.

Non-GAAP Financial Measures

This press release includes financial information prepared in accordance with GAAP, as well as other financial measures, such as Utility Margin, Adjusted Non-GAAP pretax income, Adjusted Non-GAAP net income and Adjusted Non-GAAP Diluted EPS that are considered “non-GAAP financial measures.” Generally, a non-GAAP financial measure is a numerical measure of a company’s financial performance, financial position, or cash flows that excludes (or includes) amounts that are included in (or excluded from) the most directly comparable measure calculated and presented in accordance with GAAP.

We define Utility Margin as Operating Revenues less fuel, purchased supply, and direct transmission expense (exclusive of depreciation and depletion) as presented in our Condensed Consolidated Statements of Income. This measure differs from the GAAP definition of Gross Margin due to the exclusion of Operating and maintenance, Property and other taxes, and Depreciation and depletion expenses, which are presented separately in our Condensed Consolidated Statements of Income. A reconciliation of Utility Margin to Gross Margin, the most directly comparable GAAP measure, is included in the press release above.

Management believes that Utility Margin provides a useful measure for investors and other financial statement users to analyze our financial performance in that it excludes the effect on total revenues caused by volatility in energy costs and associated regulatory mechanisms. This information is intended to enhance an investor's overall

NorthWestern Energy Reports First Quarter 2026 Financial Results

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understanding of results. Under our various state regulatory mechanisms, as detailed below, our supply costs are generally collected from customers. In addition, Utility Margin is used by us to determine whether we are collecting the appropriate amount of energy costs from customers to allow for recovery of operating costs, as well as to analyze how changes in loads (due to weather, economic, or other conditions), rates, and other factors impact our results of operations. Our Utility Margin measure may not be comparable to that of other companies' presentations or more useful than the GAAP information provided elsewhere in this report.

Management also believes the presentation of Adjusted Non-GAAP pre-tax income, Adjusted Non-GAAP net income, and Adjusted Non-GAAP Diluted EPS is more representative of normal earnings than GAAP pre-tax income, net income, and EPS due to the exclusion (or inclusion) of certain impacts that are not reflective of ongoing earnings. The presentation of these non-GAAP measures is intended to supplement investors' understanding of our financial performance and not to replace other GAAP measures as an indicator of actual operating performance. Our measures may not be comparable to other companies' similarly titled measures.

Special Note Regarding Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the “safe harbor” provisions of the Private Securities Litigation Reform Act of 1995, including, without limitation, the information under "Adjusted Non-GAAP Earnings." Forward-looking statements involve risks and uncertainties, which could cause actual results or outcomes to differ materially from those expressed. We caution that while we make such statements in good faith and believe such statements are based on reasonable assumptions, including without limitation, management's examination of historical operating trends, data contained in records, and other data available from third parties, we cannot assure you that we will achieve our projections. Factors that may cause such differences include, but are not limited to:

•risks relating to the pending merger transaction pursuant to that certain Agreement and Plan of Merger dated August 18, 2025 (Merger Agreement) between NorthWestern and Black Hills Corporation (Black Hills), including, among others, (1) the risk of delays in consummating the pending merger transaction, including as a result of required regulatory approvals, which may not be obtained on the expected timeline, or at all, (2) the risk of any event, change or other circumstance that could give rise to the termination of the Merger Agreement, (3) the risk that required regulatory approvals are subject to conditions not anticipated by NorthWestern and Black Hills, (4) the possibility that the anticipated benefits and projected value creation of the pending merger transaction will not be realized or will not be realized within the expected time period, (5) disruption to the parties’ businesses as a result of the announcement and pendency of the merger transaction, including potential distraction of management from current plans and operations of NorthWestern or Black Hills and the ability of NorthWestern or Black Hills to retain and hire key personnel, (6) reputational risk and the reaction of each company’s customers, suppliers, employees or other business partners to the pending merger transaction, (7) the possibility that the pending merger transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events, (8) the outcome of any legal or regulatory proceedings that may be instituted against NorthWestern or Black Hills related to the Merger Agreement or the pending merger transaction, (9) the risks associated with third party contracts containing consent and/or other provisions that may be triggered by the pending merger transaction, (10) legislative, regulatory, political, market, economic and other conditions, developments and uncertainties affecting NorthWestern's or Black Hills' businesses; (11) the evolving legal, regulatory and tax regimes under which NorthWestern and Black Hills operate; (12) restrictions during the pendency of the merger transaction that may impact NorthWestern's or Black Hills' ability to pursue certain business opportunities or strategic transactions; and (13) unpredictability and severity of catastrophic events, including, but not limited to, extreme weather, natural disasters, acts of terrorism or outbreak of war or hostilities, as well as NorthWestern's and Black Hills' response to any of the aforementioned factors;

•adverse determinations by regulators, such as adverse outcomes from the denial of interim rates, final rates not consistent with a reasonable ability to earn our allowed returns, failure to timely approve our requests associated with recovering the operating costs for the additional interests in Colstrip Units 3 and 4, as well

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as potential adverse federal, state, or local legislation or regulation, including costs of compliance with existing and future environmental requirements, and wildfire damages in excess of liability insurance coverage, could have a material effect on our liquidity, results of operations and financial condition;

•our ability to attract and serve large new load customers, including data centers and other energy-intensive operations, depends on regulatory and legislative actions supportive of a framework for review and approval of these large new load customer contracts.

•our ability to enter agreements to sell excess capacity and associated energy from additional interests in Colstrip Units 3 and 4 on favorable commercial and economic terms;

•the impact of extraordinary external events and natural disasters, such as a wide-spread or global pandemic, geopolitical events, earthquake, flood, drought, lightning, weather, wind, and fire, could have a material effect on our liquidity, results of operations and financial condition;

•acts of terrorism, cybersecurity attacks, data security breaches, or other malicious acts that cause damage to our generation, transmission, or distribution facilities, information technology systems, or result in the release of confidential customer, employee, or Company information;

•supply chain constraints, tariffs on certain imported products, recent high levels of inflation for products, services and labor costs, and their impact on capital expenditures, operating activities, and/or our ability to safely and reliably serve our customers;

•changes in availability of trade credit, creditworthiness of counterparties, usage, commodity prices, fuel supply costs or availability due to higher demand, shortages, weather conditions, transportation problems or other developments, may reduce revenues or may increase operating costs, each of which could adversely affect our liquidity and results of operations;

•unscheduled generation outages or forced reductions in output, maintenance or repairs, which may reduce revenues and increase operating costs or may require additional capital expenditures or other increased operating costs; and

•adverse changes in general economic and competitive conditions in the U.S. financial markets and in our service territories.

Additional factors which could affect future results of NorthWestern and Black Hills can be found in NorthWestern Energy’s Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, and Black Hills’ Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, in each case filed with the SEC and available on the SEC’s website at http://www.sec.gov. NorthWestern and Black Hills disclaim any obligation and do not intend to update or revise any forward-looking statements contained in this communication, which speak only as of the date hereof, whether as a result of new information, future events or otherwise, except as required by federal securities laws.

No Offer or Solicitation

This document is for informational purposes only and is not intended to and shall not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended.

Important Information and Where to Find It

Black Hills filed a registration statement on Form S-4 (No. 333-293105) with the SEC on January 30, 2026 to register the shares of Black Hill’s capital stock that will be issued to NorthWestern stockholders in connection with the proposed transaction. The registration statement was declared effective on February 6, 2026, at which time Black Hills filed a final prospectus and NorthWestern filed a definitive proxy statement. Black Hills and NorthWestern commenced mailing of the joint proxy statement/prospectus to their respective stockholders on or about February 10, 2026. Investors and security holders are urged to read the registration statement and joint proxy statement/prospectus (and any other documents filed with the SEC in connection with the transaction or

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incorporated by reference into the joint proxy statement/prospectus) because such documents contain important information regarding the proposed transaction and related matters. Investors and security holders may obtain free copies of these documents and other documents filed with the SEC by NorthWestern or Black Hills through the website maintained by the SEC at http://www.sec.gov or by contacting the investor relations department of NorthWestern or Black Hills at travis.meyer@northwestern.com or investorrelations@blackhillscorp.com, respectively.

Before making any investment decision, investors and security holders of NorthWestern and Black Hills are urged to read carefully the entire registration statement and joint proxy statement/prospectus, including any amendments thereto when they become available (and any other documents filed with the SEC in connection with the transaction), because they contain or will contain important information about the proposed transaction. Free copies of these documents may be obtained as described above.

Participants in Solicitation

NorthWestern, Black Hills and certain of their directors and executive officers may be deemed participants in the solicitation of proxies from the stockholders of each of NorthWestern and Black Hills in connection with the proposed transaction. Information regarding the directors and executive officers of NorthWestern and Black Hills and other persons who may be deemed participants in the solicitation of the stockholders of NorthWestern or of Black Hills in connection with the proposed transaction is included in the joint proxy statement/prospectus related to the proposed transaction, which was filed with the SEC on February 6, 2026. Information about the directors and executive officers of NorthWestern and their ownership of NorthWestern common stock can also be found in NorthWestern’s filings with the SEC, including its Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was filed on February 12, 2026, under the header “Information About Our Executive Officers” and its Proxy Statement on Schedule 14A, which was filed on March 12, 2026, under the headers “Election of Directors” and “Who Owns our Stock”. Information about the directors and executive officers of Black Hills and their ownership of Black Hills common stock can also be found in Black Hills’ filings with the SEC, including its Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was filed on February 11, 2026, under the header “Information About Our Executive Officers,” and its Proxy Statement on Schedule 14A, which was filed on March 18, 2026, under the headers “Election of Directors” and “Security Ownership of Management and Principal Shareholders,” and other documents subsequently filed by Black Hills with the SEC. To the extent any such person's ownership of NorthWestern’s or Black Hills’ securities, respectively, has changed since the filing of such proxy statement, such changes have been or will be reflected on Forms 3, 4 or 5 filed with the SEC. Additional information regarding the interests of such participants are included in the joint proxy statement/prospectus and other relevant documents regarding the proposed transaction filed with the SEC.

Investor Relations Contact: Media Contact:

Travis Meyer (605) 978-2967 Jo Dee Black (866) 622-8081

travis.meyer@northwestern.com jodee.black@northwestern.com

Annual Meeting of Shareholders April 30, 2026

NWE’s President & CEO – Brian Bird Brian Bird • Current position since January 2023 • President & Chief Operating Officer 2021-2022 • Chief Financial Officer 2003-2021 • Board member since January 2023 • 25-plus years energy and utility industry experience • Serves on Board of Directors for the following organizations: Energy Insurance Mutual, North Central Electric Association (Past President), University of Idaho Utility Executive Course (Former Board Member), Feeding South Dakota (Former Board Member), Sioux Empire United Way (Former Board Member & Campaign Chair) • Former CFO and Principal of Insight Energy, VP and Treasurer of NRG Energy, and held financial positions with the following companies: Land O’ Lakes, Northwest Airlines, Minnesota Viking Ventures, and Deluxe Corporation • Earned MBA in Finance from the University of Minnesota and double major undergraduate degree in Accounting and Finance from the University of Wisconsin – Eau Claire. Holds a Certified Public Accounting certificate 2

Experienced and Engaged Board of Directors 3 Linda Sullivan Board Chair Dave Goodin Director Sherina Maye Edwards Director Brian Bird Director, President & Chief Executive Officer Britt Ide Director Kent Larson Director Mahvash Yazdi Director Jeffrey Yingling Director Compensation (Chair), Operations Independent Joined December 2019 Independent Joined April 2017 Non-Independent Joined January 2023 Governance, Compensation Independent Joined April 2023 Audit, Operations Independent Joined December 2024 Audit, Operations Independent Joined July 2022 Jan Horsfall Director Operations (Chair), Audit Independent Joined April 2015 Audit (Chair), Governance Independent Joined October 2019 Governance (Chair), Compensation Independent Joined April 2017

Strong Executive Team 4 Crystal Lail VP & Chief Financial Officer Shannon Heim General Counsel & VP – Federal Government Affairs Brian Bird President & Chief Executive Officer Bleau LaFave VP – Asset Management & Business Development Jason Merkel VP - Distribution Bobbi Schroeppel VP – Customer Care, Communications, & Human Resources Jeanne Vold VP - Technology Joined company in 2020, current position since 2023 Joined company in 2003, current position since 2021 (formerly VP and Chief Accounting Officer ’20-’21) Current position since 2023 (formerly President & Chief Operating Officer ’21-’22 and Chief Financial Officer ’03-’21) Joined company in 1993, current position since 2022 Joined company in 1994, current position since 2023 (formerly Director of Long-Term Resources ‘12-’23) Joined company in 1998, current position since 2002 Joined company in 1999, current position since 2021 (formerly Business Technology Officer ‘12-’21)

5 “We would like to thank John Hines and Mike Cashell for their combined 60+ years of dedicated service to NorthWestern. John’s leadership over two decades, most recently as Vice President of Supply and Montana Government Affairs, played a critical role in rebuilding our generation portfolio in Montana and shaping our energy future. Mike’s remarkable 40-year career, most recently serving as Vice President of Transmission, greatly strengthened our operational foundation and reinforced a culture rooted in safety, reliability, and trust. Their insight, leadership, and commitment have contributed significantly to the success of this company and to the benefit of our shareholders, customers, and employees. We are deeply grateful for their service and wish them both the very best in retirement. - Brian Bird, CEO Thank you and Farewell to John Hines and Mike Cashell

NWE’s Auditors – Deloitte & Touche LLP 6 • Independent registered public accounting firm • Deloitte provides the following services for more than 20 industries: • Risk & Financial Advisory • Audit & Assurance • Consulting • Tax • Merger & Acquisition • Artificial Intelligence and Analytics • Cloud • Deloitte and its subsidiaries have over 470,000 professionals

NWE’s Board Chair Linda Sullivan • Director since April 27, 2017 • Retired Executive Vice President and Chief Financial Officer (CFO) of American Water Works Company, Inc., the largest publicly traded U.S. water and wastewater utility (2014-19) • 22 years of experience with Edison International Companies, last serving as Senior Vice President and CFO at Southern California Edison (2009-14) • 35-plus years of utility, finance, and regulatory experience • Certified Public Accountant (inactive) and Certified Management Accountant • Serves on the board of directors for PPL Corporation, a regulated energy company (NYSE: PPL) Meeting Agenda • Call to Order • Secretary’s Report • Declaration of Quorum • Statement of Business • Voting • Company Presentation • Report of Preliminary Voting Results • Adjournment 7

Corporate Secretary’s Report 8 Report • Affidavit of distribution for the proxy materials • Registered holders of common stock of the Company • Establishment of a quorum

Items of Business to be Considered 9 Election of Directors • Our Board is nominating nine people to serve as directors for one year, until the next annual meeting of shareholders (or until a successor is able to serve) or, if earlier, the consummation of the NWE-BKH Merger. Ratification of Deloitte & Touche LLP, as Independent Registered Public Accounting Firm for 2026 • Our Audit Committee oversees the integrity of our accounting, financial reporting, and auditing processes. To assist with those responsibilities, the committee has appointed Deloitte & Touche LLP as our independent registered public accounting firm to audit our financial statements for 2026. Advisory Vote to Approve Named Executive Officer Compensation • Our Board will consider the guidance received by the say-on-pay vote when determining executive pay for the remainder of 2026 and beyond. Proposal No. 1 Proposal No. 2 Proposal No. 3

Electronic Voting 10 • If you have not voted: Please use the virtual meeting voting platform to cast your vote now. • If you previously voted but want to change your vote: Please use the virtual meeting voting platform to cast your new vote now.

Forward-Looking Statements 11 Brian Bird President & CEO Information in this communication, other than statements of historical facts, may constitute forward-looking statements, within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements include, but are not limited to, statements about the benefits of the proposed transaction between NorthWestern and Black Hills, including future financial and operating results (including the anticipated impact of the transaction on NorthWestern’s and Black Hills’ respective earnings), statements related to the expected timing of the completion of the transaction, the plans, objectives, expectations and intentions of either company or of the combined company following the merger, anticipated future results of either company or of the combined company following the merger, the anticipated benefits and strategic and financial rationale of the merger, including estimated rate bases, investment opportunities, cash flows and capital expenditure rates and other statements that are not historical facts. Forward-looking statements may be identified by terminology such as “may,” “will,” “should,” “targets,” “scheduled,” “plans,” “intends,” “goal,” “anticipates,” “expects,” “believes,” “forecasts,” “outlook,” “estimates,” “potential,” or “continue” or negatives of such terms or other comparable terminology. The forward-looking statements are based on NorthWestern and Black Hills’ current expectations, plans and estimates. NorthWestern and Black Hills believe these assumptions to be reasonable, but there is no assurance that they will prove to be accurate. All forward-looking statements are subject to risks, uncertainties and other factors that may cause the actual results, performance or achievements of NorthWestern or Black Hills to differ materially from any results expressed or implied by such forward-looking statements. Such factors include, among others, (1) the risk of delays in consummating the potential transaction, including as a result of required regulatory and shareholder approvals, which may not be obtained on the expected timeline, or at all, (2) the risk of any event, change or other circumstance that could give rise to the termination of the merger agreement, (3) the risk that required regulatory approvals are subject to conditions not anticipated by NorthWestern and Black Hills, (4) the possibility that any of the anticipated benefits and projected synergies of the potential transaction will not be realized or will not be realized within the expected time period, (5) disruption to the parties’ businesses as a result of the announcement and pendency of the transaction, including potential distraction of management from current plans and operations of NorthWestern or Black Hills and the ability of NorthWestern or Black Hills to retain and hire key personnel, (6) reputational risk and the reaction of each company’s customers, suppliers, employees or other business partners to the transaction, (7) the possibility that the transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events, (8) the outcome of any legal or regulatory proceedings that may be instituted against NorthWestern or Black Hills related to the merger agreement or the transaction, (9) the risks associated with third party contracts containing consent and/or other provisions that may be triggered by the proposed transaction, (10) legislative, regulatory, political, market, economic and other conditions, developments and uncertainties affecting NorthWestern’s and Black Hills’ businesses; (11) the evolving legal, regulatory and tax regimes under which NorthWestern and Black Hills operate; (12) restrictions during the pendency of the proposed transaction that may impact NorthWestern’s or Black Hills’ ability to pursue certain business opportunities or strategic transactions; and (13) unpredictability and severity of catastrophic events, including, but not limited to, extreme weather, natural disasters, acts of terrorism or outbreak of war or hostilities, as well as NorthWestern’s and Black Hills’ response to any of the aforementioned factors. Additional factors which could affect future results of NorthWestern and Black Hills can be found in NorthWestern Energy’s Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, and Black Hills’ Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, in each case filed with the SEC and available on the SEC’s website at http://www.sec.gov. NorthWestern and Black Hills disclaim any obligation and do not intend to update or revise any forward-looking statements contained in this communication, which speak only as of the date hereof, whether as a result of new information, future events or otherwise, except as required by federal securities laws.

NorthWestern Energy Group, Inc. dba: NorthWestern Energy Ticker: NWE (Nasdaq) www.northwesternenergy.com Corporate Support Office 3010 West 69th Street Sioux Falls, SD 57108 (605) 978-2900 Director - Corporate Development & Investor Relations Officer Travis Meyer 605-978-2967 travis.meyer@northwestern.com 12 Guiding Principles

NWE – An Investment for the Long Term 13 • Recent rate reviews aid earnings, cash flow, and balance sheet strength • NOLs and tax credits expected to mitigate future cash tax obligations into 2029 • History of consistent annual dividend growth • 100% pure electric and natural gas utility with over 100 years of operating history • Solid economic indicators in service territory • Diverse electric supply portfolio ~52% hydro, wind, & solar Pure Electric & Gas Utility Solid Utility Foundation Earnings & Cash Flow Attractive Future Growth Prospects Financial Goals & Metrics Best Practices Corporate Governance • Residential electric and gas rates below national average • Solid system reliability • Solid JD Power Overall Customer Satisfaction scores • Disciplined maintenance capital investment program • Data centers and other new large-load opportunities • FERC regional transmission • Incremental generating capacity (subject to successful resource procurement bids) • Target 4%-6% EPS growth plus dividend yield to provide competitive total return • Target dividend long-term payout ratio of 60%-70% • Target debt to capitalization ratio of 50%-55% with liquidity of $100 million or greater 5th Best Governance Score Recognized by EEI for our emergency response efforts following the July 2024 windstorm in Missoula, MT

About NorthWestern 14 Montana Operations Electric 440,700 customers 25,542 miles – transmission & distribution lines 1,660 MW maximum capacity owned power generation Natural Gas 249,400 customers 8,072 miles of transmission and distribution pipeline 17.85 Bcf of gas storage capacity Own 25.3 Bcf of proven natural gas reserves Nebraska Operations Natural Gas 43,400 customers 836 miles of distribution pipeline Data as of 12/31/2025 South Dakota Operations Electric 65,600 customers 3,730 miles – transmission & distribution lines 420 MW nameplate owned power generation Natural Gas 51,200 customers 1,908 miles of transmission and distribution pipeline

About Our Company 15 850,300 Customers MT – 690,100 SD/NE – 160,200 1,667 Employees MT – 1,353 SD/NE - 314 339 Communities in Montana and South Dakota with electric service MT – 223 (99 electric only / 124 combo) SD – 116 (74 electric only / 42 combo) 234 Communities in Montana, South Dakota, and Nebraska with natural gas service MT – 148 (24 gas only / 124 combo) SD – 82 (40 gas only / 42 combo) NE – 4 gas communities $5.6 Billion Rate Base MT - $4.6 billion SD/NE – $1.0 billion $548.6 Million Capital Expenditures in 2025 MT - $448.6 million SD/NE - $100.0 million $8.5 Billion Total Assets MT – $7.0 billion SD/NE – $1.5 billion $174.2 million Property Taxes MT – $167.4 million SD/NE – $6.8 million Lone Peak, Big Sky, MTData as of December 31, 2025

A Diversified Electric and Gas Utility 16 NorthWestern’s ‘80/20’ rules: Approximately 80% Electric and 80% Montana. Nearly $5.6 billion of rate base investment to serve our customers. Data as reported in our 2025 10-K

2025 - Year In Review Executing on Strategic Initiatives • Announced agreement with Black Hills Corporation for an all-stock Merger of Equals o To create a premier regional regulated electric and natural gas utility company • Closed acquisition of Avista and Puget Colstrip interests o Providing resource adequacy in Montana, increasing plant ownership from 15% to 55%, and supporting potential large-load integration • Submitted $300M (131MW) South Dakota natural gas project to SPP’s expedited resource adequacy study • Acquired Energy West and Cut Bank Gas natural gas distribution assets Legislative & Regulatory Outcomes • Montana SB301 signed into law, providing greater confidence for transmission investment in Montana • Montana HB490 signed into law which clarifies and limits wildfire-related risks, protecting our customers, communities, and investors • Approval of Wildfire Mitigation Plan in Montana • Completed Montana Electric & Natural Gas general rate reviews o Providing recovery of our significant investment to reliably serve our customers Advancing Data Center Growth Opportunities • Signed third letter of intent with Quantica for a 500+ megawatt data center • Progressed Sabey letter of intent to a development agreement 17 Powerhouse at Hauser Dam on the Missouri River (near Helena, Montana) Missoula, Montana Lake McDonald, Montana

18 Merger with Black Hills Benefits Stakeholders Strategic combination represents a highly attractive value creation opportunity for both companies. Increases Scale Position and Growth Increases the combined company target EPS growth rate to 5-7%, supported by the doubling of each company’s rate base to total of ~$11 bn with significant growth opportunities Expands Investment Opportunity Leverages enhanced resources to make strategic investments that foster economic development, including addressing the growing demand for energy, including from data centers Substantial Long-Term Value for Customers Enhances Business Diversity Delivering energy to more than 2.1 mm customers across multiple contiguous jurisdictions, served by a highly skilled workforce focused on safety and reliability Strengthens Balance Sheet Strong and predictable cash flows support a customer-focused capital investment program while producing high-quality, investment- grade credit metrics Bringing together two complementary teams focused on reliability and exceptional customer service to deliver even greater value. For more information, see www.blackhillsnorthwesternbettertogether.com

8% to 10% Total Return >10% Total Return Incremental Opportunities: > 6% EPS Growth Approximately 4% Dividend Yield Base Capital Plan: 4% to 6% EPS Growth ✓ Data centers & new large- load opportunities ✓ FERC Regional Transmission ✓ Incremental generating capacity (subject to successful resource procurement bids) $3.21 billion of highly executable and low-risk capital investment forecasted over the next five years. This investment is expected to drive annualized earnings and rate base growth of approximately 4% - 6%. + The NorthWestern Value Proposition + 19 = = 2026-2030 Capital Investment ($ Millions)

Reliability 99.979% Uninterrupted Reliability In 2024 and 2025, our System Average Interruption Duration Index (SAIDI) performance was 110.4 and 111.6 minutes, respectively, ranking in the second quartile compared to other utilities. In 2025, our customers enjoyed uninterrupted power 99.979% of the time on average*. Exceeding industry reliability standards… a remarkable achievement given our rural, rugged, and dispersed service territory. * System Average Interruption Duration Index (SAIDI) is the total number of minutes interruption the average customer experiences. The numbers shown here reflect data reported to IEEE, including planned outages but excluding Major Event Days and Catastrophic Events per IEEE methodology. 20

Affordability * Electric - EEI Typical Bills and Average Summer and Winter Rates Reports 2008-2025 ** Natural Gas - EIA U.S. Price of Natural Gas Delivered to Residential Customers 2008-2025 Utility Bills Below National Average Keeping energy bills low… empowering our customers and communities to thrive. 21

Sustainability Based on MWh's supplied from owned & long-term contracted resources. Contracted Coke & Waste Tailings as well as much of the contracted wind, hydro and solar are federally mandated Qualifying Facilities, as defined under the Public Utility Regulatory Policies Act of 1978 (PURPA). NorthWestern does not own all the renewable energy certificates (RECs) generated by contracted resources and periodically sells its own RECs with proceeds benefiting retail customers. Accordingly, we cannot represent that 100% of carbon-free energy in the portfolio was delivered to our customers. Highly Carbon-Free Supply Portfolio 52% Carbon-Free Portfolio Exceeds 41% National Average* * EIA.gov Table 7.2B Electric Net Generation: U.S. Electric Power Sector - 2024 22

The Incredible Value of Electricity & Natural Gas Compared to the cost of other niceties of your daily life, the necessity of powering your home remains an incredible value. Coffee / Latte Heat, Cool, Power, & Protect Your Entire Home $4 - $5 per day Cell Phone Bill Family of 4 $6 - $7 per day (Electricity ~$4/day & Natural Gas ~$2-$3/day)*$5 - $11 per day McDonald’s Big Mac Meal $10 - $12 per meal Party-Sized Bag of Ruffles $7 - $8 per bag 23 * Based on NWE’s typical monthly bill data for our average residential electric and natural gas customers, respectively.

Conclusion Pure Electric & Gas Utility Solid Utility Foundation Best Practices Corporate Governance Attractive Future Growth Prospects Strong Earnings & Cash Flows 24

Preliminary Results 25 1. Election of Directors 2. Ratification of Deloitte & Touche LLP, as Independent Registered Public Accounting Firm for 2026 3. Advisory Vote to Approve Named Executive Officer Compensation   

Thank youDelivering a bright future 26

First Quarter Earnings Webinar April 30, 2026 8-K Date: April 30, 2026

Forward-Looking Statements 2 Information in this communication, other than statements of historical facts, may constitute forward-looking statements, within the meaning of Section 27A of the Securities Act of 1933, as amended, and Section 21E of the Securities Exchange Act of 1934, as amended. These statements include, but are not limited to, statements about the benefits of the proposed transaction between NorthWestern and Black Hills, including future financial and operating results (including the anticipated impact of the transaction on NorthWestern’s and Black Hills’ respective earnings), statements related to the expected timing of the completion of the transaction, the plans, objectives, expectations and intentions of either company or of the combined company following the merger, anticipated future results of either company or of the combined company following the merger, the anticipated benefits and strategic and financial rationale of the merger, including estimated rate bases, investment opportunities, cash flows and capital expenditure rates and other statements that are not historical facts. Forward-looking statements may be identified by terminology such as “may,” “will,” “should,” “targets,” “scheduled,” “plans,” “intends,” “goal,” “anticipates,” “expects,” “believes,” “forecasts,” “outlook,” “estimates,” “potential,” or “continue” or negatives of such terms or other comparable terminology. The forward-looking statements are based on NorthWestern and Black Hills’ current expectations, plans and estimates. NorthWestern and Black Hills believe these assumptions to be reasonable, but there is no assurance that they will prove to be accurate. All forward-looking statements are subject to risks, uncertainties and other factors that may cause the actual results, performance or achievements of NorthWestern or Black Hills to differ materially from any results expressed or implied by such forward-looking statements. Such factors include, among others, (1) the risk of delays in consummating the potential transaction, including as a result of required regulatory and shareholder approvals, which may not be obtained on the expected timeline, or at all, (2) the risk of any event, change or other circumstance that could give rise to the termination of the merger agreement, (3) the risk that required regulatory approvals are subject to conditions not anticipated by NorthWestern and Black Hills, (4) the possibility that any of the anticipated benefits and projected synergies of the potential transaction will not be realized or will not be realized within the expected time period, (5) disruption to the parties’ businesses as a result of the announcement and pendency of the transaction, including potential distraction of management from current plans and operations of NorthWestern or Black Hills and the ability of NorthWestern or Black Hills to retain and hire key personnel, (6) reputational risk and the reaction of each company’s customers, suppliers, employees or other business partners to the transaction, (7) the possibility that the transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events, (8) the outcome of any legal or regulatory proceedings that may be instituted against NorthWestern or Black Hills related to the merger agreement or the transaction, (9) the risks associated with third party contracts containing consent and/or other provisions that may be triggered by the proposed transaction, (10) legislative, regulatory, political, market, economic and other conditions, developments and uncertainties affecting NorthWestern’s and Black Hills’ businesses; (11) the evolving legal, regulatory and tax regimes under which NorthWestern and Black Hills operate; (12) restrictions during the pendency of the proposed transaction that may impact NorthWestern’s or Black Hills’ ability to pursue certain business opportunities or strategic transactions; and (13) unpredictability and severity of catastrophic events, including, but not limited to, extreme weather, natural disasters, acts of terrorism or outbreak of war or hostilities, as well as NorthWestern’s and Black Hills’ response to any of the aforementioned factors. Additional factors which could affect future results of NorthWestern and Black Hills can be found in NorthWestern Energy’s Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, and Black Hills’ Annual Report on Form 10-K, Quarterly Reports on Form 10-Q, and Current Reports on Form 8-K, in each case filed with the SEC and available on the SEC’s website at http://www.sec.gov. NorthWestern and Black Hills disclaim any obligation and do not intend to update or revise any forward-looking statements contained in this communication, which speak only as of the date hereof, whether as a result of new information, future events or otherwise, except as required by federal securities laws. See Appendix for Additional Merger Related Disclosures.

NorthWestern Energy 3 NorthWestern Energy Group, Inc. dba: NorthWestern Energy Ticker: NWE (Nasdaq) www.northwesternenergy.com Corporate Support Office 3010 West 69th Street Sioux Falls, SD 57108 (605) 978-2900 Director - Corporate Development & Investor Relations Officer Travis Meyer 605-978-2967 travis.meyer@northwestern.com

Recent Highlights ✓ Reported GAAP diluted EPS of $1.03 o Non-GAAP diluted EPS of $1.311 o Affirming 2026 earnings guidance range of $3.68 - $3.832 o Affirming long-term rate base and EPS growth rates targets of 4% - 6%3 ✓ Merger Progress o Received shareholder approval of NWE-BKH merger proposals o Constructive settlements reached with certain key intervenors in Montana, Nebraska, and South Dakota merger dockets ✓ Regulatory & Legislative o Constructive wildfire legislation passed in South Dakota4 o Submitted a Large New Load tariff rule proposal with the MPSC ✓ Data Centers: Signed Development Agreement with Quantica Infrastructure5 ✓ Dividend Declared: $0.67 per share payable June 30, 2026 (June 15 record date) (1) See slides “First Quarter 2026 Non-GAAP Earnings” and “Non-GAAP Financial Measures” that follow. (2) See “Strong Growth Outlook” slide that follows for major assumptions included in guidance. (3) Based on 2024 Adjusted Diluted Non-GAAP EPS of $3.40 and 2024 estimated rate base of $5.38 billion. See “Non-GAAP Financial Measures” slide in appendix for additional information. (4) See “South Dakota Wildfire Bill” slide that follows for additional information. (5) See “Large-Load Customers” slide that follows for additional information. 4 Near Bozeman, Montana

Thank youFirst Quarter Financial Review 5

First Quarter 2026 Financial Results 6 (1) Utility Margin is a non- GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. Note: Subtotal variances may exist due to rounding.

First Quarter EPS vs Prior Period • GAAP: $0.22 or (17.6)% • Non-GAAP1: $0.09 or 7.4% First Quarter Net Income vs Prior Period • GAAP: $13.4 or (17.4)% • Non-GAAP1: $5.3 or 7.0% First Quarter 2026 Financial Results 7 (1) See “First Quarter 2026 Non-GAAP Earnings” and “Non-GAAP Financial Measures” slides that follow.

First Quarter 2026 Earnings Drivers 8 (1) Utility Margin is a non-GAAP measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. (2) See “First Quarter 2026 Non-GAAP Earnings” and “Non-GAAP Financial Measures” slides that follow. After-Tax EPS vs Prior Year The decrease in GAAP diluted EPS for the quarter vs prior year was primarily due to retail volumes and operating expenses, including merger- related costs and incremental Colstrip operating costs, partly offset by an improvement in Utility Margin primarily due to a Montana electric base rates increase.

First Quarter 2026 Utility Margin Bridge 9 Pre-Tax Millions vs Prior Year Note: Utility Margin is a non-GAAP measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. (1) Including a $3.2 million increase due to acquisition of Energy West Operations. $15.0 million or 4.6% increase in Utility Margin items that impact Net Income

We estimate weather to be a $14.4 million pre-tax detriment as compared to normal, and a $16.6 million detriment as compared to first quarter 2025. (1) As a result of the adoption of Accounting Standard Update 2017-07 in March 2018, pension and other employee benefit expense is now disaggregated on the GAAP income statement with portions now recorded in both OG&A expense and Other (Expense) Income lines. To facilitate better understanding of trends in year-over-year comparisons, the non-GAAP adjustment above re-aggregates the expense in OG&A - as it was historically presented prior to the ASU 2017-07 (with no impact to net income or earnings per share). (2) Certain merger-related costs are not tax- deductible. (3) Power prices in the Pacific Northwest associated with the designated power sales contracts included within our temporary PCCAM tariff waiver were insufficient to recover the operating expenses associated with the Avista Interests. (4) Utility Margin is a non-GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. First Quarter 2026 Non-GAAP Earnings 10 Note: Subtotal variances may exist due to rounding.

11 Affirming 2026 Non-GAAP EPS Guidance of $3.68 - $3.83 per diluted share ✓ Affirming long-term growth rate from 2024 base1 • EPS growth of 4% to 6% • Rate base growth of 4% to 6% • Continued focus on closing the gap between earned & authorized returns ✓ $3.2 billion 5-year capital plan including approximately $300 million of investment for generation development in South Dakota ✓ Cash from operations and debt to fund base capital plan. Equity issuances expected beginning in 2027 to fund South Dakota generation investment ✓ Targeting FFO / Debt > 14% (1) Based on 2024 Adjusted Diluted Non-GAAP EPS of $3.40 and 2024 estimated rate base of $5.38 billion. See “Non-GAAP Financial Measures” slide in appendix for additional information. Strong Growth Outlook This guidance range is based upon, but not limited to, the following major assumptions: • Normal weather in our service territories; • Excludes costs related to the pending merger with Black Hills Corp.; • Approval of PCCAM waiver and power prices sufficient to recover operating expense from incremental Avista and Puget Colstrip interests; • An effective income tax rate of approximately 14%-18%; and • Diluted average shares outstanding of approximately 61.7 million.

Highly diversified, executable, and low-risk critical capital investment plan. Regulated Utility Five-Year Capital Plan (millions) 12

Thank youBusiness Updates 13

14 South Dakota Wildfire Bill No Strict Liability: • Strict liability cannot be applied to utility operations alleged to have caused wildfire-related damages Legal Protections for Providers: • Rebuttable presumption that a valid and current wildfire mitigation plan is reasonable preparation for, and mitigation of, wildfire risk (burden of proof rests on plaintiffs) • 4-year statute of limitations from date of initial ignition of the wildfire Damages: • Economic: Property damages (including real property, personal property, livestock, and crops) and monetary losses (such as loss of business income) • Noneconomic: Only if death or bodily injury occurs • Punitive: Only with clear & convincing evidence of willful and wanton misconduct NorthWestern plans to submit a Wildfire Mitigation Plan for SDPUC approval in the second half of 2026 and expects to update the plan every two years going forward. SB 36 was passed by the South Dakota Legislature with broad bipartisan support in both the House (63-2) and Senate (31-3) and has been signed into law. The new law clarifies and limits wildfire-related liability risks, protecting our customers, communities, and investors.

15 Merger with Black Hills Benefits Stakeholders Strategic combination represents a highly attractive value creation opportunity for both companies. Increases Scale Position and Growth Increases the combined company target EPS growth rate to 5-7%, supported by the doubling of each company’s rate base to total of ~$11 bn with significant growth opportunities Expands Investment Opportunity Leverages enhanced resources to make strategic investments that foster economic development, including addressing the growing demand for energy, including from data centers Substantial Long-Term Value for Customers Enhances Business Diversity Delivering energy to more than 2.1 mm customers across multiple contiguous jurisdictions, served by a highly skilled workforce focused on safety and reliability Strengthens Balance Sheet Strong and predictable cash flows support a customer-focused capital investment program while producing high-quality, investment- grade credit metrics Bringing together two complementary teams focused on reliability and exceptional customer service to deliver even greater value. For more information, see www.blackhillsnorthwesternbettertogether.com

Merger with Black Hills Timeline 16 ✓ Filed joint applications for approval in Montana, Nebraska, and South Dakota in Q4 2025 ✓ Nebraska hearing held on April 7, 2026; final order anticipated in Q2 2026 ✓ Settlements reached with certain key intervenors in Montana, Nebraska, and South Dakota o Montana and South Dakota hearings are scheduled to commence on May 12th and June 22nd, respectively ✓ Filed joint application with FERC on December 22, 2025 o Federal Power Act provides 180 days for approval with extension for good cause ✓ Filed S-4/Joint Proxy Statement on January 30, 2026 ✓ Shareholder approvals received by both companies on April 2, 2026 ✓ Filed Hart-Scott-Rodino on March 20, 2026 ✓ The 30-day waiting period expired on April 20, 2026, satisfying a U.S. antitrust condition to closing

17 Data Center Process (Montana & South Dakota) Data Center Request • Load & Location • Supply Potential • Customer/Developer Required Timing Queue Count: 8 High-Level Assessment • Viability Assessment • Southwest Power Pool Screening • High Level Cost Estimate Queue Count: 4 Energy Service Agreement (ESA) • Regulatory Approvals (as needed) • Contract Signing • Business Development Handoff Queue Count: 0 Construction • Project Management Assignment • Construction Kick-Off • Supply Development • Generation Build Process Queue Count: 0 Letter of Intent (LOI) • Supply Development Estimates • Development Agreement Negotiations Development Agreement • Development Deposit to Fund Studies: - Montana: System Impact Study & Facility Study - South Dakota: Southwest Power Pool Delivery Point Network Study Queue Count: 3 Queue Count: 0

✓ Montana ▪ Expected to be served by overall utility portfolio, which is long capacity beginning in 2026 ▪ Diversified and highly carbon-free generating portfolio ▪ Submitted a Large New Load tariff rule proposal with the MPSC in March 2026 ✓ South Dakota ▪ Significant indications of interest ▪ Any new large-load customers would require incremental capacity with infrastructure rider to provide generation cost recovery ▪ South Dakota PUC has an established process for large-load customers with a deviated rate tariff 18 Large-Load Customers Montana Large-Load Opportunities ✓ Confidentially Announced: December 17, 2024 ▪ Company: Sabey Data Centers ▪ Study Load: 50 MW ramping to 200 MW ▪ Targeted Start Date: Mid-2028 ▪ Agreement Status: Letter of Intent + Development Agreement ✓ Announced: December 19, 2024 ▪ Company: Atlas Power ▪ Study Load: 75 MW ramping to 150 MW ▪ Targeted Start Date: Late 2027 ▪ Agreement Status: Letter of Intent + Development Agreement ✓ Announced: July 30, 2025 ▪ Company: Quantica Infrastructure ▪ Study Load: 25 MW ramping to 1,100 MW ▪ Targeted Start Date: Early 2029 ▪ Agreement Status: Letter of Intent + Development Agreement Filed Development Agreement signed

Colstrip Transaction Overview 19 Announcement: Effective Date: Capacity: Acquisition Price: Status Update: Puget July 2024 December 31, 2025 370 MW (185 MW each of units 3 & 4) $0.0 Signed contract in October 2025 to sell the dispatchable capacity and associated energy through late 2027. Revenue from the contract is expected to largely offset the ~$30 million of incremental annual operating costs resulting from the transfer. Filed with FERC for cost- based rates in October 2025, with approval received in February 2026 retroactive to January 1, 2026. Avista January 2023 December 31, 2025 222 MW (111 MW each of units 3 & 4) $0.0 Filed a temporary PCCAM tariff waiver request with the MPSC in August 2025 that would provide a near-term cost-recovery mechanism to offset a portion of the ~$18.0 million of incremental annual operating costs resulting from the transfer. The waiver was temporarily granted in January 2026. NorthWestern’s acquisition of Avista and Puget’s 592 MW of additional Colstrip capacity: • Avista interests advance our regulated portfolio to resource adequacy and increase facility ownership from 15% to 30% • Puget interests move ownership from 30% to 55% which provides the ability to determine strategic direction and investment decisions at the facility • Combined interests support the integration of large-load customers, delivering substantial benefits to our customers, communities, and investors Avista and Puget Sound will remain responsible for their respective pre-closing share of environmental, asset retirement obligations, and pension liabilities attributed to events or conditions existing prior to the closing of the transaction and for any future decommissioning and demolition costs associated with the existing facilities that comprise their interests

8% to 10% Total Return >10% Total Return Incremental Opportunities: > 6% EPS Growth Approximately 4% Dividend Yield Base Capital Plan: 4% to 6% EPS Growth ✓ Data centers & new large- load opportunities ✓ FERC Regional Transmission ✓ Incremental generating capacity (subject to successful resource procurement bids) $3.21 billion of highly diversified, executable and low-risk critical capital investment forecasted over the next five years. This investment is expected to drive annualized earnings and rate base growth of approximately 4% - 6%. + The NorthWestern Value Proposition + 20 = = 2026-2030 Capital Investment ($ Millions)

Conclusion Pure Electric & Gas Utility Solid Utility Foundation Best Practices Corporate Governance Attractive Future Growth Prospects Strong Earnings & Cash Flows 21 The pending merger with Black Hills Corporation will combine the strengths of both companies, resulting in an organization with greater scale, financial stability, and operational expertise and is designed to create a stronger, more resilient energy company focused on delivering safe, reliable, and affordable energy solutions to customers.

Thank youAppendix: 22

(1) The revenue requirement associated with the FERC regulated portion of Montana electric transmission and ancillary services are included as revenue credits to our MPSC jurisdictional customers. Therefore, we do not separately reflect FERC authorized rate base or authorized returns. (2) The Montana gas revenue requirement includes a step-down which approximates annual depletion of our natural gas production assets included in rate base. (3) This jurisdiction was acquired in 2025 as part of the acquisition of Energy West Operations. (4) This table excludes insignificant jurisdictions for Montana propane delivery, Havre Pipeline Company, and Cut Bank Gas natural gas delivery. (5) For those items marked as "n/a," the respective settlement and/or order was not specific as to these terms. Coal Generation Rate Base as a percentage of Total Rate Base Revenue from coal generation is not easily identifiable due to the use of bundled rates in South Dakota and other rate design and accounting considerations. However, NorthWestern is a fully regulated utility company for which rate base is the primary driver of earnings. The data to the left illustrates that NorthWestern only derives approximately 8-10% of earnings from its jointly owned coal generation rate base. Rate Base & Authorized Return Summary Appendix 23

First Quarter 2026 Financial Results 24 (1) Utility Margin is a non- GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. Note: Subtotal variances may exist due to rounding. Appendix

Utility Margin (Q1) ($ in millions) Three Months Ended March 31, 2026 2025 Variance Electric $ 271.8 $ 242.7 $ 29.1 12.0% Natural Gas 80.2 85.7 (5.5) (6.4%) Total Utility Margin1 $ 352.0 $ 328.4 $ 23.6 7.2% (1) Utility Margin is a non-GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. Increase in utility margin due to the following factors: $ 23.7 Base rates 5.5 Electric margin from the acquisition of the Puget Interests 2.2 Transmission revenue due to market conditions and rates 2.0 Non-recoverable Montana electric supply costs (12.2) Electric retail volumes (6.2) Natural gas retail volumes (including a $3.2 million increase due to acquisition of Energy West Operations) (3.3) Montana property tax tracker collections (0.7) Natural gas production step down 4.0 Other $ 15.0 Change in Utility Margin Impacting Net Income $ 5.2 Property & other taxes recovered in revenue, offset in property & other taxes 2.6 Production tax credits, offset in income tax expense 0.8 Operating expenses recovered in revenue, offset in operating & maintenance expense $ 8.6 Change in Utility Margin Offset Within Net Income $ 23.6 Increase in Consolidated Utility Margin 25 Appendix Note: Subtotal variances may exist due to rounding.

Operating Expenses (Q1) Increase in operating expenses due to the following factors: $ 10.1 Electric generation maintenance (Including $6.4 million and $3.9 million due to the acquisition of the Puget Interests and Avista Interests, respectively) 4.4 Depreciation expense due to plant additions and higher depreciation rates 3.5 Labor and benefits(1) 3.4 Merger-related costs, including consulting and legal fees 2.0 Property and other taxes not recoverable within trackers 1.9 Wildfire mitigation expense, partly offset by higher base revenues 0.7 Insurance expense, primarily due to increased wildfire risk premiums 0.5 Uncollectible accounts 0.2 Technology implementation and maintenance expenses 3.1 Other $ 29.8 Change in Operating Expense Items Impacting Net Income ($ in millions) Three Months Ended March 31, 2026 2025 Variance Operating & maintenance $ 74.5 $ 56.7 $ 17.8 31.4% Administrative & general 46.1 41.4 4.7 11.4% Property & other taxes 50.4 43.2 7.2 16.7% Depreciation & depletion 66.8 62.4 4.4 7.1% Total Operating Expenses* $ 237.8 $ 203.7 $ 34.1 16.7% $ 5.2 Property and other taxes recovered in trackers, offset in revenue 0.8 Operating and maintenance expenses recovered in trackers, offset in revenue (0.7) Pension and other postretirement benefits, offset in other income(1) (1.0) Deferred compensation, offset in other income $ 4.3 Change in Operating Expense Items Offset Within Net Income $ 34.1 Increase in Operating Expenses* *Excluding fuel, purchased supply, and direct transmission expense. (1) In order to present the total change in labor and benefits, we have included the change in the non-service cost component of our pension and other postretirement benefits, which is recorded within other income on our Condensed Consolidated Statements of Income. This change is offset within this table as it does not affect our operating expenses. 26 Appendix

Operating to Net Income (Q1) ($ in millions) Three Months Ended March 31, 2026 2025 Variance Operating Income $ 114.1 $ 124.7 ($10.6) (8.5%) Interest expense, net (39.9) (36.5) 3.4 9.3% Other income, net 3.1 3.9 (0.8) (20.5%) Income Before Income Taxes 77.3 92.1 (14.8) (16.1%) Income tax expense (13.8) (15.2) (1.4) (9.2%) Net Income $ 63.5 $ 76.9 ($13.4) (17.4%) 27 Appendix Note: Subtotal variances may exist due to rounding.

Tax Reconciliation (Q1) 28 Appendix

Segment Results (Q1) 29 Appendix *Direct transmission expense excludes depreciation and depletion. (1) Utility Margin is a non-GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. (2) Consists of unallocated corporate costs, including merger-related costs, and certain limited unregulated activity within the energy industry.

Electric Segment (Q1) (1) Utility Margin is a non-GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure. 30 Appendix

Natural Gas Segment (Q1) 31 Appendix (1) Utility Margin is a non-GAAP Measure. See appendix slide titled “Reconciling Gross Margin to Utility Margin” for additional disclosure.

Cash from Operating Activities increased by $6.0 million. The increase in cash provided by working capital is primarily due to a decrease in our net cash outflows for energy supply costs, as shown in the table below. Funds from Operations decreased by $15.1 million over prior period. Net Under-Collected Supply Costs ($ in millions) Beginning (Jan. 1) Ending (Mar. 31) Inflow / (Outflow) 2025 $5.9 $25.6 ($19.7) 2026 $44.8 $53.4 ($8.6) 2026 Decrease in Net Cash Outflows $11.1 First Quarter 2026 Cash Flow 32 No Planned Equity Issuances in 2026 Financing plans (targeting a FFO to Debt ratio > 14%) are expected to maintain our current credit ratings and are subject to change Debt financing in 2026 • Amended our existing NorthWestern Energy Group $150 million term loan to extend the maturity date from April 10, 2026 to December 31, 2026 • Priced $150 million, 5.51% coupon, 10-year South Dakota First Mortgage Bonds expected to be issued on June 15, 2026 Appendix

Balance Sheet 33 Appendix Debt to Total Capitalization slightly down from last quarter and inside our targeted 50% - 55% range.

Reconciling Gross Margin to Utility Margin Management believes that Utility Margin provides a useful measure for investors and other financial statement users to analyze our financial performance in that it excludes the effect on total revenues caused by volatility in energy costs and associated regulatory mechanisms. This information is intended to enhance an investor's overall understanding of results. Under our various state regulatory mechanisms, our supply costs are generally collected from customers. In addition, Utility Margin is used by us to determine whether we are collecting the appropriate amount of energy costs from customers to allow recovery of operating costs, as well as to analyze how changes in loads (due to weather, economic or other conditions), rates and other factors impact our results of operations. Our Utility Margin measure may not be comparable to that of other companies' presentations or more useful than the GAAP information provided elsewhere in this report. Note: Subtotal variances may exist due to rounding. (1) Utility Margin is a non-GAAP Measure. 34 Appendix

PCCAM Impact by Quarter 35 Appendix Pre-Tax $ Millions – Shareholder (Detriment) Benefit Note: Subtotal variances may exist due to rounding.

Qualified Facility Earnings Adjustment Our electric QF liability consists of unrecoverable costs associated with contracts covered under PURPA that are part of a 2002 stipulation with the MPSC and other parties. Risks / losses associated with these contracts are born by shareholders, not customers. Therefore, any mitigation of prior losses and / or benefits of liability reduction also accrue to shareholders. 36 Appendix

Non-GAAP Financial Measures 37 Appendix Pre-Tax Adjustments ($ Millions) 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 Reported GAAP Pre-Tax Income 156.5$ 176.1$ 178.3$ 182.2$ 144.2$ 190.2$ 182.4$ 201.6$ 214.7$ 187.6$ Non-GAAP Adjustments to Pre-Tax Income: Weather 15.2 (3.4) (1.3) (7.3) 9.8 1.1 (8.9) 4.3 10.6 14.4 Lost revenue recovery related to prior periods (14.2) - - - - - - - - - QF liability adjustment - - (17.5) - - (6.9) - - - - Electric tracker disallowance of prior period costs 12.2 - - - 9.9 - - - - - Income tax adjustment - - 9.4 - - - - - - - Community Renewable Energy Project Penalty - - - - - - 2.5 - (2.3) 1.3 Impairment of Alternative Energy Storage Investment - - - - - - - - 4.2 - NWE-BKH Merger Transaction Costs (not tax deductible) - - - - - - - - - 9.3 Regulatory Disallowance of Certain YCGS Capital Costs - - - - - - - - - 31.2 Remove Q4 2025 PCCAM Expense Following Suspension of 90/10 Sharing - - - - - - - - - 2.3 Adjusted Non-GAAP Pre-Tax Income 169.7$ 172.7$ 168.9$ 174.9$ 163.9$ 184.4$ 176.0$ 205.9$ 227.2$ 246.1$ Tax Adjustments to Non-GAAP Items ($ Millions) 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 GAAP Net Income 164.2$ 162.7$ 197.0$ 202.1$ 155.2$ 186.8$ 183.0$ 194.1$ 224.1$ 181.1$ Non-GAAP Adjustments Taxed at 38.5% (12'-17') and 25.3% (18'-current): Weather 9.3 (2.1) (1.0) (5.5) 7.3 0.8 (6.6) 3.2 7.9 10.8 Lost revenue recovery related to prior periods (8.7) - - - - - - - - - QF liability adjustment - - (13.1) - - (5.2) - - - - Electric tracker disallowance of prior period costs 7.5 - - - 7.4 - - - - - Income tax adjustment (12.5) - (12.8) (22.8) - - - - - - Community Renewable Energy Project Penalty - - - - - - 2.5 - (2.3) 1.3 Previously claimed AMT credit - - - - - - - 3.2 - - Release of Unrecognized Tax Benefit - - - - - - - (3.2) (16.9) (7.4) Impairment of Alternative Energy Storage Investment - - - - - - - - 3.1 - Natural Gas Safe Harbor Method Change - - - - - - - - (7.0) - NWE-BKH Merger Transaction Costs (not tax deductible) - - - - - - - - - 9.3 Regulatory Disallowance of Certain YCGS Capital Costs - - - - - - - - - 23.3 Remove Q4 2025 PCCAM Expense Following Suspension of 90/10 Sharing - - - - - - - - - 1.7 Non-GAAP Net Income 159.8$ 160.6$ 170.1$ 173.8$ 169.9$ 182.4$ 178.9$ 197.3$ 208.9$ 220.1$ Non-GAAP Diluted Earnings per Share 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 Diluted Average Shares (Millions) 48.5 48.7 50.2 50.8 50.7 51.9 56.3 60.4 61.4 61.5 Reported GAAP Diluted Earnings per Share 3.39$ 3.34$ 3.92$ 3.98$ 3.06$ 3.60$ 3.25$ 3.22$ 3.65$ 2.94$ Non-GAAP Adjustments: Weather 0.19 (0.04) (0.02) (0.11) 0.14 0.01 (0.11) 0.05 0.13 0.18 Lost revenue recovery related to prior periods (0.18) - - - - - - - - - QF liability adjustment - - (0.26) - - (0.10) - - - - Electric tracker disallowance of prior period costs 0.16 - - - 0.15 - - - - - Income tax adjustment (0.26) - (0.25) (0.45) - - - - - - Community Renewable Energy Project Penalty - - - - - - 0.04 - (0.04) 0.02 Previously claimed AMT credit - - - - - - - 0.05 - - Release of Unrecognized Tax Benefit - - - - - - - (0.05) (0.28) (0.12) Impairment of Alternative Energy Storage Investment - - - - - - - - 0.05 - Natural Gas Safe Harbor Method Change - - - - - - - - (0.11) - NWE-BKH Merger Transaction Costs (not tax deductible) - - - - - - - - - 0.15 Regulatory Disallowance of Certain YCGS Capital Costs - - - - - - - - - 0.38 Remove Q4 2025 PCCAM Expense Following Suspension of 90/10 Sharing - - - - - - - - - 0.03 Non-GAAP Diluted Earnings per Share 3.30$ 3.30$ 3.39$ 3.42$ 3.35$ 3.51$ 3.18$ 3.27$ 3.40$ 3.58$

Non-GAAP Financial Measures This presentation includes financial information prepared in accordance with GAAP, as well as other financial measures, such as Utility Margin, Adjusted Non-GAAP pretax income, Adjusted Non-GAAP net income and Adjusted Non-GAAP Diluted EPS that are considered “non-GAAP financial measures.” Generally, a non-GAAP financial measure is a numerical measure of a company’s financial performance, financial position or cash flows that excludes (or includes) amounts that are included in (or excluded from) the most directly comparable measure calculated and presented in accordance with GAAP. We define Utility Margin as Operating Revenues less fuel, purchased supply and direct transmission expense (exclusive of depreciation and depletion) as presented in our Consolidated Statements of Income. This measure differs from the GAAP definition of Gross Margin due to the exclusion of Operating and maintenance, Property and other taxes, and Depreciation and depletion expenses, which are presented separately in our Consolidated Statements of Income. A reconciliation of Utility Margin to Gross Margin, the most directly comparable GAAP measure, is included in this presentation. Management believes that Utility Margin provides a useful measure for investors and other financial statement users to analyze our financial performance in that it excludes the effect on total revenues caused by volatility in energy costs and associated regulatory mechanisms. This information is intended to enhance an investor's overall understanding of results. Under our various state regulatory mechanisms, our supply costs are generally collected from customers. In addition, Utility Margin is used by us to determine whether we are collecting the appropriate amount of energy costs from customers to allow recovery of operating costs, as well as to analyze how changes in loads (due to weather, economic or other conditions), rates and other factors impact our results of operations. Our Utility Margin measure may not be comparable to that of other companies' presentations or more useful than the GAAP information provided elsewhere in this report. Management also believes the presentation of Adjusted Non-GAAP pre-tax income, Adjusted Non-GAAP net income and Adjusted Non-GAAP Diluted EPS is more representative of normal earnings than GAAP pre-tax income, net income and EPS due to the exclusion (or inclusion) of certain impacts that are not reflective of ongoing earnings. The presentation of these non-GAAP measures is intended to supplement investors' understanding of our financial performance and not to replace other GAAP measures as an indicator of actual operating performance. Our measures may not be comparable to other companies' similarly titled measures. 38 Appendix

Additional Merger Related Disclosures 39 Appendix No Offer or Solicitation This document is for informational purposes only and is not intended to and shall not constitute an offer to buy or sell or the solicitation of an offer to buy or sell any securities, or a solicitation of any vote or approval, nor shall there be any sale of securities in any jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such jurisdiction. No offering of securities shall be made, except by means of a prospectus meeting the requirements of Section 10 of the U.S. Securities Act of 1933, as amended. Important Information and Where to Find It Black Hills filed a registration statement on Form S-4 (No. 333-293105) with the SEC on January 30, 2026 to register the shares of Black Hill’s capital stock that will be issued to NorthWestern stockholders in connection with the proposed transaction. The registration statement was declared effective on February 6, 2026, at which time Black Hills filed a final prospectus and NorthWestern filed a definitive proxy statement. Black Hills and NorthWestern commenced mailing of the joint proxy statement/prospectus to their respective stockholders on or about February 10, 2026. Investors and security holders are urged to read the registration statement and joint proxy statement/prospectus (and any other documents filed with the SEC in connection with the transaction or incorporated by reference into the joint proxy statement/prospectus) because such documents contain important information regarding the proposed transaction and related matters. Investors and security holders may obtain free copies of these documents and other documents filed with the SEC by NorthWestern or Black Hills through the website maintained by the SEC at http://www.sec.gov or by contacting the investor relations department of NorthWestern or Black Hills at travis.meyer@northwestern.com or investorrelations@blackhillscorp.com, respectively. Before making any investment decision, investors and security holders of NorthWestern and Black Hills are urged to read carefully the entire registration statement and joint proxy statement/prospectus, including any amendments thereto when they become available (and any other documents filed with the SEC in connection with the transaction), because they contain or will contain important information about the proposed transaction. Free copies of these documents may be obtained as described above. Participants in Solicitation NorthWestern, Black Hills and certain of their directors and executive officers may be deemed participants in the solicitation of proxies from the stockholders of each of NorthWestern and Black Hills in connection with the proposed transaction. Information regarding the directors and executive officers of NorthWestern and Black Hills and other persons who may be deemed participants in the solicitation of the stockholders of NorthWestern or of Black Hills in connection with the proposed transaction is included in the joint proxy statement/prospectus related to the proposed transaction, which was filed with the SEC on February 6, 2026. Information about the directors and executive officers of NorthWestern and their ownership of NorthWestern common stock can also be found in NorthWestern’s filings with the SEC, including its Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was filed on February 12, 2026, under the header “Information About Our Executive Officers” and its Proxy Statement on Schedule 14A, which was filed on March 12, 2026, under the headers “Election of Directors” and “Who Owns our Stock”. Information about the directors and executive officers of Black Hills and their ownership of Black Hills common stock can also be found in Black Hills’ filings with the SEC, including its Annual Report on Form 10-K for the fiscal year ended December 31, 2025, which was filed on February 11, 2026, under the header “Information About Our Executive Officers,” and its Proxy Statement on Schedule 14A, which was filed on March 18, 2026, under the headers “Election of Directors” and “Security Ownership of Management and Principal Shareholders,” and other documents subsequently filed by Black Hills with the SEC. To the extent any such person's ownership of NorthWestern’s or Black Hills’ securities, respectively, has changed since the filing of such proxy statement, such changes have been or will be reflected on Forms 3, 4 or 5 filed with the SEC. Additional information regarding the interests of such participants are included in the joint proxy statement/prospectus and other relevant documents regarding the proposed transaction filed with the SEC.

Thank youDelivering a bright future 40

Source: View Original Filing on SEC EDGAR

FAQ

How did NorthWestern Energy (NWE) perform financially in Q1 2026?

NorthWestern Energy’s Q1 2026 GAAP net income was $63.5 million, down from $76.9 million, with diluted EPS falling to $1.03 from $1.25. However, adjusted non-GAAP diluted EPS rose to $1.31 from $1.22 as rate increases and higher utility margin offset cost pressures.

What earnings guidance did NorthWestern Energy (NWE) reaffirm for 2026?

NorthWestern reaffirmed 2026 non-GAAP earnings guidance of $3.68 to $3.83 per diluted share. This outlook assumes normal weather, excludes merger-related costs, relies on PCCAM waiver approval, expects an effective tax rate of 14–18%, and uses about 61.7 million diluted shares outstanding.

What is the status of NorthWestern Energy’s merger with Black Hills Corporation?

NorthWestern and Black Hills have shareholder approval for their all-stock merger of equals, and the Hart-Scott-Rodino waiting period has expired. They reached settlements with certain key intervenors in Montana, Nebraska, and South Dakota, with remaining state commission hearings scheduled in Q2 2026 and closing targeted second-half 2026.

How is NorthWestern Energy investing for future growth between 2026 and 2030?

NorthWestern plans about $3.2 billion of capital investment from 2026 to 2030, supporting 4–6% annual rate base growth from a 2024 base of approximately $5.4 billion. The plan includes a record $683 million 2026 capital program and roughly $300 million for a 131 MW South Dakota gas facility.

What dividend did NorthWestern Energy declare and what is its payout objective?

NorthWestern declared a quarterly dividend of $0.67 per share, payable June 30, 2026, to shareholders of record on June 15, 2026. The company aims to maintain a long-term dividend payout ratio between 60% and 70% of earnings, balancing shareholder returns with capital needs.

How did Colstrip acquisitions affect NorthWestern Energy’s Q1 2026 results?

NorthWestern completed acquisitions of Avista’s 222 MW and Puget’s 370 MW interests in Colstrip Units 3 and 4 on January 1, 2026. These added operating and maintenance costs and contributed to higher expenses, while Puget interests increased electric margin and ownership to 55%, enhancing strategic control over the facility.

What recent regulatory and legislative developments impact NorthWestern Energy (NWE)?

Recent developments include South Dakota’s Senate Bill 36, which narrows wildfire-related liability and recognizes approved mitigation plans, and Montana’s Large New Load tariff proposal. NorthWestern also continues to navigate PCCAM cost sharing changes and rate review outcomes affecting cost recovery and future earnings.

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NorthWestern Energy (Nasdaq: NWE) posts Q1 2026 results and advances Black Hills merger

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FAQ

How did NorthWestern Energy (NWE) perform financially in Q1 2026?

What earnings guidance did NorthWestern Energy (NWE) reaffirm for 2026?

What is the status of NorthWestern Energy’s merger with Black Hills Corporation?

How is NorthWestern Energy investing for future growth between 2026 and 2030?

What dividend did NorthWestern Energy declare and what is its payout objective?

How did Colstrip acquisitions affect NorthWestern Energy’s Q1 2026 results?

What recent regulatory and legislative developments impact NorthWestern Energy (NWE)?

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NorthWestern Energy (Nasdaq: NWE) posts Q1 2026 results and advances Black Hills merger

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8-K Event Classification

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FAQ

How did NorthWestern Energy (NWE) perform financially in Q1 2026?

What earnings guidance did NorthWestern Energy (NWE) reaffirm for 2026?

What is the status of NorthWestern Energy’s merger with Black Hills Corporation?

How is NorthWestern Energy investing for future growth between 2026 and 2030?

What dividend did NorthWestern Energy declare and what is its payout objective?

How did Colstrip acquisitions affect NorthWestern Energy’s Q1 2026 results?

What recent regulatory and legislative developments impact NorthWestern Energy (NWE)?

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