But this was only a break from the heat, not long-term relief, forecasters said.
In Portland, temperatures will rebound into the upper 90s on Tuesday and highs will reach the mid-80s later in the week, said Clinton Rockey, a meteorologist with the National Weather Service in Portland. Temperatures will still be 10 to 20 degrees above average at least until next Tuesday.
“That said, it’s a heck of a lot better than being 30 to 40 degrees above normal,” Mr. Rockey said.
While tying a single heat wave to climate change requires extensive attribution analysis, heat waves around the world are growing more frequent, longer lasting and more dangerous. The 2018 National Climate Assessment, a major scientific report issued by 13 federal agencies, notes that the number of hot days is increasing. And the frequency of heat waves in the United States jumped from an average of two per year in the 1960s to six per year by the 2010s. Also, the season for heat waves has stretched to be 45 days longer than it was in the 1960s, according to the report.
It is all part of an overall warming trend: The seven warmest years in the history of accurate worldwide record-keeping have been the last seven years, and 19 of the 20 warmest years have occurred since 2000; worldwide, June 2019 was the hottest June ever recorded, and June 2020 essentially tied it.
Last year tied with 2016 as the hottest year on record, according to one analysis.
The oppressive heat that settled in the Pacific Northwest was the result of a wide and deep mass of high-pressure air that, because of a wavy jet stream, parked itself over much of the region. Known as a heat dome, such an enormous high-pressure zone acts like a lid, trapping heat so it accumulates.
Matthew Cullen, a National Weather Service meteorologist in Seattle, said that Tuesday should be the last day of extreme heat in that city, with temperatures expected to hit 95 degrees, 20 degrees hotter than normal.