An unrelenting heat wave that may have led to at least seven deaths weighed down on the Pacific Northwest on Sunday as temperatures were expected to soar again into the triple digits. 

The National Weather Service issued an excessive heat warning for more than 10 million people across Washington, Oregon, Idaho and Northern California on Sunday. Temperatures were forecast to reach as high as 103 degrees and surpass more than a dozen daily heat records in the region.

Why is the heat significant? Saturday tied a record with six consecutive days of temperatures over 95 degrees for the Portland region, weather service meteorologist Shawn Weagle said. Temperatures ranged from 15 to 22 degrees above normal, according to the weather service. 

Deadly heat waves become more frequent. In 2021, a deadly heat wave led to about 800 deaths in Oregon, Washington and British Columbia during late June and early July because of a heat dome weather phenomenon that prompted record temperatures.

When will the heat subside? Forecasters expect the heat to wane for the Pacific Northwest on Monday as a storm brings cooler air, returning the area to more normal temperatures by Tuesday or Wednesday.

More coverage of the heat wave:

Deadly, record-breaking heat across Washington, Oregon, Idaho

Dozens of cities and towns from Washington to Oregon to Montana broke or far exceeded daily heat records over the weekend.

On Friday, Missoula reached 102 degrees, breaking its daily heat record for July 29. Redding, California, hit a daily record high of 114 degrees, and Medford, Oregon, hit 114, shattering its 2009 daily record of 109 and falling 1 degree short of tying an all-time high for the city.