‘Big time warm up,’ smoke on the way to Western Washington

Another heat wave is on the way to Western Washington late this week, with temperatures across the region expected to range between the mid to upper 90s.

While the National Weather Service says that conditions will “not be as hot as it was at the end of June,” an excessive heat watch is in place starting Wednesday afternoon. That’s when a ridge of high pressure is expected to strengthen, resulting in what the NWS calls a “big time warm up.”

Highs in the mid-90s in the Seattle area are expected on both Thursday and Friday, with “low 100s possible in the warmest locations,” the NWS predicts. Despite that, KIRO 7 meteorologist Morgan Palmer also notes that the potential for weaker offshore wind flow could help the region “avoid triple digit temperatures.”

Temperatures will then start to descend into the low 90s on Saturday, and then back into the 80s by Sunday.

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Extreme heat isn’t the only concern for forecasters, with wildfire smoke also expected to move west over the Cascades. The extent of that smoke’s effect on air quality remains unclear, but “a stronger offshore flow would flood more bad air into our region,” Palmer warns.

That said, the arrival of additional smoke from the state’s southern border could also help tamp down higher temperatures.

“Another fly in the forecast ointment is whether a thick canopy of California wildfire smoke will move into the area aloft,” Palmer outlines in his forecast for this week. “Distant smoke like that doesn’t do as much as home-grown smoke to harm surface air quality, but it could be a significant sun shade for us.”

“If we do get thick smoke aloft, it could cut five degrees or more off the daytime high temperatures during the worst of the heat wave,” he adds.