contains: 1. Historical financial statements of NorthWestern filed in accordance with Rule 3-05 of Regulation S-X, included as Exhibit 99.1, which are incorporated herein by reference; and 2. Pro forma financial information of Black Hills and NorthWestern on a combined basis in accordance with Article 11 of Regulation S-X giving effect to certain pro forma adjustments related to the pending merger transaction as if it were completed on January 1, 2025 as it relates to the pro forma combined c…

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

contains: 1. Historical financial statements of NorthWestern filed in accordance with Rule 3-05 of Regulation S-X, included as Exhibit 99.1, which are incorporated herein by reference; and 2. Pro forma financial information of Black Hills and NorthWestern on a combined basis in accordance with Article 11 of Regulation S-X giving effect to certain pro forma adjustments related to the pending merger transaction as if it were completed on January 1, 2025 as it relates to the pro forma combined c…

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

contains: 1. Historical financial statements of NorthWestern filed in accordance with Rule 3-05 of Regulation S-X, included as Exhibit 99.1, which are incorporated herein by reference; 2. Pro forma financial information of Black Hills and NorthWestern on a combined basis in accordance with Article 11 of Regulation S-X giving effect to certain pro forma adjustments related to the pending merger transaction as if it were completed on January 1, 2025 as it relates to the pro forma combined conde…

Results of Operations and Financial Condition. On Feb. 4, 2026, Black Hills Corporation ("the Company") issued a press release announcing financial results for the fourth quarter of 2025. The press release is attached as Exhibit 99.1 to this Form 8-K. A copy of the Company's presentation is attached as Exhibit 99.2 to this report. This information is being furnished pursuant to

Results of Operations and Financial Condition. On Nov. 5, 2025, Black Hills Corporation ("the Company") issued a press release announcing financial results for the third quarter of 2025. The press release is attached as Exhibit 99.1 to this Form 8-K. A copy of the Company's presentation is attached as Exhibit 99.2 to this report. This information is being furnished pursuant to

Entry into a Material Definitive Agreement. The disclosure under

Other Events. Completion of Debt Offering On October 2, 2025, Black Hills Corporation (the “ Company ” or “ we ”) issued and sold an aggregate principal amount of $450 million of its 4.550% Notes due 2031 (the “ Notes ”). The Notes were issued and sold pursuant to the previously disclosed Underwriting Agreement entered into on September 25, 2025 by the Company and the representative of the several underwriters named in Schedule A thereto (the “ Underwriting Agreement ”). The Notes were offere…

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The disclosure under

Entry into a Material Definitive Agreement. On September 25, 2025, Black Hills Corporation (the “ Company ” or “ we ”) entered into an Underwriting Agreement by and between the Company and the representative of the several underwriters named in Schedule A thereto (the “ Underwriting Agreement ”), pursuant to which the Company has agreed to issue and sell and the underwriters have severally agreed to purchase an aggregate principal amount of $450 million of its 4.550% Notes due 2031 (the “ Not…

contains: 1. Historical financial statements of NorthWestern filed in accordance with Rule 3-05 of Regulation S-X, included as Exhibits 99.1 and 99.2, which are incorporated herein by reference; 2. Pro forma financial information of Black Hills and NorthWestern on a combined basis in accordance with Article 11 of Regulation S-X giving effect to certain pro forma adjustments related to the pending merger transaction as if it were completed on January 1, 2024 as it relates to the pro forma comb…

Entry into a Material Definitive Agreement. On August 18, 2025, Black Hills Corporation, a South Dakota corporation (“ Black Hills ” or the “ Company ”), entered into an Agreement and Plan of Merger (the “ Merger Agreement ”) with NorthWestern Energy Group, Inc., a Delaware corporation (“ NorthWestern ”) and River Merger Sub Inc., a Delaware corporation and direct wholly owned subsidiary of Black Hills (“ Merger Sub ”). The Merger Agreement, which has been unanimously approved by both the boa…

CEO — Linden R. Evans: The current CEO is retiring in an orderly succession to a named successor (Brian B. Bird) as part of a merger, which constitutes a planned transition rather than a sudden loss of leadership.

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

Entry into a Material Definitive Agreement. As previously disclosed , on June 16, 2023, Black Hills Corporation, a South Dakota corporation (the “ Company ”), entered into an Equity Distribution Sales Agreement (the “ Existing Sales Agreement ”), by and among (a) the Company, (b) each of Bank of Montreal, Bank of America, N.A., MUFG Securities EMEA plc, Mizuho Markets Americas LLC, and Royal Bank of Canada (each a “ Forward Purchaser ” and together, the “ Forward Purchasers ”), (c) each of BM…

CFO — Erik Keller: The filing discloses the resignation of the Senior Vice President and Chief Information Officer, which is a genuine departure of a senior executive, though the role is not the CEO or CFO.

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

Director — Mark A. Schober: The filing discloses the planned retirement of a long-serving director at the next annual meeting, which is an orderly succession rather than a sudden loss of a senior executive.

Senior Vice President, General Counsel and Chief Compliance Officer — Brian Iverson: The General Counsel is departing to accept an external role, which is a genuine loss of a senior officer, though the initial announcement was a planned retirement.

of Form 8-K and 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 liabilities of that section, nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, except as shall be expressly set forth by specific reference in such filing.

Creation of a Direct Financial Obligation or an Obligation under an Off-Balance Sheet Arrangement of a Registrant. The disclosure under

Entry into a Material Definitive Agreement. On May 31, 2024, the Company entered into a Second Amendment to Fourth Amended and Restated Credit Agreement, among Black Hills Corporation, as Borrower, the financial institutions party thereto, as Banks, and U.S. Bank National Association, as Administrative Agent (the “Amended Revolver”). The Amended Revolver extends the term from July 19, 2026 to May 31, 2029, with two one-year extension options (subject to consent from the lenders). The Amended…