Seattle is cooling down from a heat wave. Well, if you consider that a heat wave.
Temperatures reached 94 degrees at Seattle-Tacoma International Airport on Wednesday — the hottest day of 2025, so far. Tuesday topped out at 88 degrees.
The forecast for the heatwave prompted us to ask our readers, “What exactly is a ‘heat wave’ in Seattle?”
The consensus? Most of you said our sizzling temperatures this week would have counted, but there was no widely agreed upon threshold among the more than 200 responses submitted.
“Anything above 80 degrees here is miserable,” said Brian Krupenevich, of Seattle. That was his definition of a heat wave.
For Diane Cooper, of Renton, it was 100 degrees. “I am from the desert (southwest), so unless humidity accompanies temperatures in the 90s, it’s OK with me,” she said. “I will go swimming once temps hit the 90s — otherwise too cold!”
For Tom Schwab, of Seattle, a heat wave is 77 degrees and over. For Lee Hover, of Lacey, Thurston County, originally from the New York City metropolitan area, it’s 95 degrees. For Michael Gelsey, of Edmonds, it’s three days above 84 degrees in a row.
So, what’s the “official” definition?
The National Weather Service defines a heat wave as a “period of abnormally hot weather generally lasting more than two days” with or without humidity.
If we use those metrics, Tuesday and Wednesday counted, reaching temperatures more than 10 degrees above their averages at this time of year, said Matthew Cullen, a meteorologist from Seattle’s National Weather Service office.
But Cullen understands that “abnormally hot weather” is “somewhat arbitrary, depending on who you’re asking.”
Clearly.
If we use Krupenevich and a handful of other readers’ metric of a single 80-plus-degree day to qualify as a heat wave, Seattle had 35 last year, Cullen said.
Seattle had five 90-plus-degree days in 2024 and no 100-plus-degree days since 2021.
So far, there have been 15 days above 80 degrees in 2025 and two above 90.
Like Cooper from the Southwest desert and Hover from the Northeast metro-area, people living in Washington might have different tolerances for heat depending on where they’re from.
Only 35% of those living in Seattle were born in Washington state, according to the most recent U.S. Census Bureau data.
But no matter where we’re from, our experience of the Seattle heat might be more unifying than we think.
“The mild Pacific Northwest climate makes us all sensitive to heat,” said Sharon Bogan, spokesperson for Seattle & King County Public Health.
The weather service tends to talk about heat waves more in terms of health-related impacts like heatstroke than in metrics of temperature and time, Cullen said. We’ve seen heat-related illnesses and health impacts in the Seattle area consistently for several years now, he said.
The weather service had issued a heat advisory for Wednesday and Thursday, urging people to take extra precautions if they work or spend time outside.
Heart problems, stroke and kidney failure are the most common health problems on hot days, and heat-related illnesses become more frequent even when temperatures are in the 80s when the nights aren’t cooling off, Bogan said.
The number of patients treated for heat-related illnesses in King County has increased since 2019, spiking especially in 2021 with the year’s heat dome, Bogan said. There were 153 such incidents in 2019, compared with 274 in 2024.
And things might only get worse.
Heat waves are becoming more common, lasting longer and reaching higher temperatures, said Marissa Anderson, spokesperson for the weather service and the National Oceanic and Atmospheric Administration.
The ratio of warm to cold extremes used to be one-to-one in the 1970s. But now, there are more than twice as many heat extremes as cold extremes.
Heat waves are projected to “continue increasing and their influence on human health will be exacerbated by population increase as well as by urbanization,” Anderson said, “as most of the victims tend to be in large urban areas where the heat island effect makes matters worse.”
So, no matter if it’s 80 degrees or 100, check in on your neighbors and people who you know are more vulnerable to heat-related illnesses. Plus, make sure to brush up on tips for how to keep cool and visit st.news/becool.
