Highs on Sunday could approach 100 degrees in Seattle and 107 in Portland, Ore., cities where a significant portion of the population lacks air conditioning. Seattle has only reached the century mark twice in more than 75 years of records. If Portland hits 107, it would match its highest temperature ever recorded.
The Weather Service has issued excessive-heat watches from extreme Northern California through large parts of Oregon and Washington, warning that heat-related illnesses are likely for some, with concern for residents without adequate air conditioning — “i.e. a lot of people,” the Spokane office wrote.
How the heat wave will evolve
Temperatures were already toasty Tuesday across the Columbia Basin of eastern Washington state and extreme northeast Oregon, where highs climbed into the upper 90s. That marks a mere taste of what’s to come. Wednesday and Thursday will feature similar temperatures before the mercury spikes Friday, with a few spots hitting 100.
The skyrocketing temperatures can be traced to a sprawling ridge of high pressure colloquially known as a “heat dome.” That high deflects inclement weather to the north, bringing copious sunshine, sinking air and clear skies. Weak high pressure is in control across the northwestern Lower 48 but will be replaced by a robust high-pressure system slated to move ashore and into southern British Columbia during the day Saturday.
In downtown Seattle, a high near 96 is forecast Saturday, 97 Sunday and 94 on Monday. Average highs this time of year tend toward 74.