黑山美股招股说明书(2026-02-06版)

February 6, 2026 Dear Shareholders: On behalf of the boards of directors and management teams of Black Hills Corporation (“Black Hills”) and NorthWesternEnergy Group, Inc. (“NorthWestern”), we are pleased to enclose the joint proxy statement/prospectus relating to the all-stockmerger of Black Hills and NorthWestern. Black Hills and NorthWestern have entered into a Merger Agreement, dated as ofAugust18, 2025 (the “Merger Agreement”) providing for the combination of the two companies. Under the Merger Agreement,River Merger Sub Inc., a direct wholly owned subsidiary of Black Hills (“Merger Sub”) will merge with and into NorthWestern,and NorthWestern will continue as the surviving corporation and a direct subsidiary of Black Hills (such transaction, the“Merger”). Upon completion of the Merger, Black Hills will adopt a new name reflecting the combined business, with suchname to be announced at a later date (the combined company, referred to as “Newco”). We believe the Merger will create astrong combined company that will deliver important benefits to our shareholders, to our customers and to the communities weserve. If the Merger is completed, NorthWestern shareholders will receive 0.98 validly issued, fully paid and nonassessable share ofcommon stock of Black Hills for each share of NorthWestern common stock held, as described in more detail in the enclosed jointproxy statement/prospectus under the heading “The Proposed Merger — Merger Consideration.” Black Hills will continue to list its common stock on the New York Stock Exchange or other mutually-agreed stockexchange, and Black Hills and NorthWestern will work together to agree on a new name and ticker symbol for Newco prior tothe closing of the Merger. Whether or not you plan to attend your company’s special meeting, please take the time to vote by following theinstructions on your proxy card. The dates, times and locations of the special meetings are as follows: Black Hills: Time and Date:10:00 a.m. (Mountain Time) on April2, 2026Location:The Black Hills special meeting will be held solely by virtual webcast. There will be no physical meetinglocation. NorthWestern: 11:00 a.m. (Central Time) on April2, 2026The NorthWestern special meeting will be held solely by virtual webcast. There will be no physical meeting Time and Date:Location:location. Your vote is very important regardless of the number of shares you own. We cannot complete the Merger unless shareholders ofboth Black Hills and NorthWestern approve certain proposals related to the Merger. Sincerely, Sincerely, Timothy OlsonCorporate SecretaryNorthWestern Energy Group, Inc. We urge you to read the enclosed joint proxy statement/prospectus, which includes important information about the Mergerand our special meetings.In particular, see “Risk Factors” on pages23through35of the joint proxy statement/prospectus, which contains a description of risks that you should consider in evaluating the Merger. For a discussion of the U.S. federal income tax consequences of the Merger, see “The Proposed Merger — Material U.S.Federal Income Tax Consequences of the Merger” beginning on page98of the joint proxy statement/prospectus. Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of themerger described in the joint proxy statement/prospectus or the securities to be issued pursuant to the merger under the joint proxystatement/prospectus or determined if the joint proxy statement/prospectus is accurate or adequate. Any representation to thecontrary is a criminal offense. The enclosed joint proxy statement/prospectus is dated February 6, 2026 and isfirst being mailed to shareholders of Black Hills and NorthWestern on or about February 10, 2026. Black Hills Corporation7001 Mount Rushmore RoadRapid City, South Dakota 57702(605) 721-1700 NOTICE OF SPECIAL MEETING OF SHAREHOLDERS 10:00 a.m. (Mountain Time) on April2, 2026 Time and DatePlace The Black Hills special meeting will be held solely by virtual webcast. There will be nophysical meeting location. To be admitted to the Black Hills special meeting atwww.virtualshareholdermeeting.com/BKH2026SM as a shareholder, you must enter the16-digit control number found next to the label “Control Number” on your Proxy cardor voting instruction form. ••••••To vote on a proposal to approve the issuance of shares of common stock, par value$1.00 per share, of Black Hills (“Black Hills Common Stock”), pursuant to the termsof the Agreement and Plan of Merger, dated as of August18, 2025 (the “MergerAgreement”), by and among Black Hills, River Merger Sub Inc. (“Merger Sub”), andNorthWestern Energy Group, Inc. (“NorthWestern”) (the “Black Hills IssuanceProposal”);To vote on a proposal to amend the restated articles of incorporation of Black Hills(the “Black Hills Charter”) to increase the authorized shares from 100million to300million (the “Black Hills Share Increase Proposal”);To vote on a proposal to am