Triple-Digit Heat Dome Bakes Pacific Northwest, Triggers First Blackout Triple-Digit Heat Dome Bakes Pacific Northwest, Triggers First Blackout The Pacific Northwest is experiencing a multi-day heat wave that we said last week would be " historic ." The unrelenting triple-digit temperatures shattered records across the region and have stressed out power grids where rolling blackouts have been reported. Bloomberg reports Avista Corporation, which supplies electricity to 340,000 residential, commercial, and industrial customers, triggered its first rolling blackout across its grid after it became overloaded Monday evening. Rotating outages first hit 9,300 customers late Monday and could expand as temperatures remain well above average through July 4. Avista was the first major utility to report rolling blackouts in the Northwest region, and with positive temperature anomalies to linger through the week, it may not be the last. Avista has never "experienced this kind of demand on our system and this kind of impact to our system," Heather Rosentrater, senior vice president of energy delivery at the utility company, told reporters during a press conference Monday.