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Another May heat wave: why low 80s this weekend will not break records

Tim Durkan
Tim Durkan Photography
A view from Seattle on March 6, 2020.

Temperatures around the Puget Sound region were shooting up Friday into the mid-to-upper 70s, after an already warm week. And the forecast for Mother’s Day weekend promises temperatures in the low 80s. It almost feels like summer.

But KNKX weather expert Cliff Mass says this kind of heat wave in mid- to late May is not that unusual for the region.

“So, we’ll be warm — above normal — but we’re not going to break records,” Mass says. He says for many days around this time, we’d have to get to the upper 80s or even low 90s to match or break all-time highs.

Mass says a spike of heat anywhere from about May 5 to May 20 is fairly common around here. “Almost every year we get this warm period, this heat wave,” he says.

The reason, he says, has to do with a combination of factors. First, the sun is very strong at this time of year, as we’re just a little more than a month away from the solstice, when it is at its strongest. Second, offshore or easterly flow — winds coming from the east — often come with the dynamic weather of spring. When they do, that air flows down the slopes of the Cascade Mountains and compresses and warms as it moves toward the coast.

“And that gives us the big spikes,” Mass says.

He says as we get later into May and early June, there’s a shift, when high pressure starts building up in the eastern Pacific. And it pushes marine air inland, creating the prevalence of persistent low clouds and cooler temperatures that many people dread — the so-called “June Gloom.”

“So, mid-May is a sweet spot,” Mass says. Best to get out and enjoy it, before the gloom sets in.

You can listen above to hear the full discussion. 


Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to