Ruthless Heat Wave Baking U.S. Northwest Triggers First Blackout Bloomberg 16 hrs ago Mark Chediak, Brian K. Sullivan and Josh Saul (Bloomberg) -- The unrelenting heat wave that shattered temperature records across the U.S. Pacific Northwest on Monday and threatens to smother the region for another six straight days has begun to trigger rolling blackouts in some parts. For the first time in the company’s history, Avista Corp. -- which supplies electricity to nearly 340,000 homes and businesses in the Northwest -- instituted rotating outages after parts of its system overloaded. The blackouts, which were affecting about 9,300 customers late Monday, are expected to last into Tuesday. Across all of Washington and Oregon, more than 30,000 customers were in the dark, according to PowerOutage.US, which compiles utility outage data.