Cliff Mass: This will not be ‘some historic heat wave’ as Puget Sound temps flirt with low-90s

The Puget Sound region was expected to warm up into the lower 90s on Wednesday, with the rest of the week following suit. 80-degree weather is on tap until the weekend.

“It’s going to be warming up a lot from yesterday,””It’s not going to be the end of the world, but mid-80s are possible. It cooled down quite a bit yesterday, but it’s starting to go up quickly.”

Much of the lowlands south of Seattle will get into the mid-80s, according to Cliff Mass, professor of Atmospheric Sciences at the University of Washington (UW), while it will remain a little cooler up north. A 90-degree day is on schedule in the Seattle urban area Wednesday, with temperatures even a little warmer to the south.

“Wednesday will be the warmest day of the week, clearly,” Mass told “The Jason Rantz Show.” “After that, as we get into Thursday, marine air is going to start pushing in, and temperatures will go down at least five degrees on Thursday and then get back into the 70s by the weekend.”

“So this is a little overstated,” Rantz asked Mass.

“Well, if you’re suggesting this is some historic heat wave, that is not the case,” Mass answered. “It’ll be a little bit of a warm-up. It will be above normal. Remember, normal is about 80 degrees right now. This is the warmest, driest time of the year historically in Seattle, and we’re going to get some of that.”

Mass wouldn’t go so far as to call this burst of hot weather an official “heat wave,” claiming that a heat wave needs to be more than a single day of above-normal temperatures.

Summer nighttime temperatures have increased, Axios finds

Axios Seattle reported that between 1970 and 2024, the average summer nighttime temperatures increased in 96% of 241 locations analyzed. In their findings, the average summer low in Seattle increased by 2.9 degrees, in Yakima by 4.3 degrees, and in Spokane by 5.1 degrees.

“Why do they talk about nighttime temperatures?” Mass countered. “If they talked about the daytime high temperatures, which people really care about, that’s not up so much. It’s the nighttime temperatures that are up, and that’s an issue because some of that is not real. Many urban areas are much warmer at night because of the urban heat island effect, and so that brings the nighttime temperatures up preferentially over the daytime ones.”

Onshore wind is expected to bring cooler air in later in the week, although temperatures are still estimated to be above average, hanging around the mid and upper-80s.

“The good news is, at least, it seems the air quality is pretty strong right now, right?” Rantz asked.

“The air quality actually is quite good. In fact, the fires have been less than normal,” Mass claimed. “So strangely enough, despite all these warnings about how warm it’s been and how dry it’s been and all that kind of stuff, actually, the fire situation has been extremely benign this year. We’ve seen very, very, very little or no smoke coming into the western side of the state.”

Listen to the full conversation here.

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