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L Appendix 38 Timeline of Montana Generation Portfolio Owned and Long-Term Resource Portfolio Timeline Only Carbon-Free Resources (780 MW) Added Since 2011 Owned Resources Long-Term 88 Colstrip Unit 4 222 MW DGGS Spion Kop Hydro Dams 150 MW 40 MW 446 MW** 2 MW Hydro Two Add Dot Add Reduction 11 MW 2.7 MW (3.5) MW Hydro Hydro Prior to '08 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021E 2022E Contracted CELP & Basin Judith Gap Various Various Turnbill Gordon Musselshell Fairfield Resources YELP Creek 87 MW* 52 MW & Horse- 21.5 MW 3.7 MW shoe & various 15.4 MW Butte 9.6 MW 20 MW 10 MW Greenfield Various 25 MW 17 MW 144 MW + + Stillwater, Big Timber & Various 114.7 MW South Peak 80 MW Grizzly, Apex 1 & ConEd, Black Bear, MT Sun Wheatland, Caithness & 160 MW Pondera & Beaver Creek Teton 113 MW 278 MW * CELP (Colstrip Energy Limited Partnership) contract expires in 2024 and YELP (Yellowstone Energy Limited Partnership) expires in 2028 ** Hydro dams 446 MW of normal max generation capability (439 MW Nameplate Capacity) excludes 194 MW of Kerr dam which was tonsferred to the Salish & Kootenai Tribes in 2015 NorthWestern Energy Montana - Cumulative Timeline of Owned and Contracted Electric Resources 900 Coal Natural Gas ■Hydro ■Wind ■Solar 800 700 MegaWatts 600 500 400 300 200 100 0 Clean (Hydro, Wind & Solar) vs Total Resources % Prior to 2008 2009 2008 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021E 2022E 54.4% 31.9% 31.9% 31.9% 26.5% 31.4% 33.2% 58.2% 58.2% 59.0% 59.6% 63.3% 65.3% 65.4% 73.3% 74.8% Since 2011, we have added 780 MW of generation, both owned and long-term contract, to our generation portfolio, all of which is from carbon-free resources.

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