Seattle's 'hidden 100' day and other heat wave stats

Seattle and much of the rest of Western Washington may be heading into uncharted territory as part of what's shaping up to be a potentially historic heat wave across the Northwest.

Already Seattle's official forecast high from the National Weather Service in Seattle for Sunday is 100 degrees, believed to be the first time NWS has issued a 100+ forecast for Seattle more than a day in advance.

And a check of the history books shows why. Seattle has officially only hit 100 three times before: 100 on July 16, 1941 at Downtown Federal Building, 100 again on July 20, 1994 at Sea-Tac Airport, and 103 at Sea-Tac on July 29, 2009.  

But there's a fourth triple-digit day hiding in the record books and it actually could skew our idea of what should be considered the hottest June date in the city.

It was still technically spring when the temperature zoomed to 100 at Seattle's Downtown Federal Building on June 9, 1955. Weather records had been kept at that building from 1894 to 1972 but once Sea-Tac Airport opened in 1945, NOAA moved the official Seattle reporting station there. Sea-Tac "only" reached 96 that day so that is the official temperature of record for June 9, 1955. (As a consolation prize, that day still does hold the official record high for June 9.)

As forecasts have Seattle's expected high temperatures anywhere from 96-102 this weekend, not only is Seattle's all-time record high of 103 threatened, but so is Seattle's all-time June record even if we come up shy of 103.

The June record is 98 if we use the combined official Federal Building and Sea-Tac data, set on June 25, 1925. Sea-Tac's warmest June day is 96 degrees set two other times aside from 1955, most recently in 2017.

But now you know Seattle has in fact reached 100 in June, even if the official books don't take notice. It's like if Usain Bolt ran a 9.54 100 meter dash but didn't run it at an official meet to count as a World Record. It still happened.

What other records are we chasing?

Let's finish up June by noting some other cities' records that are in jeopardy of falling: Olympia is at 101 (June 30, 1942), Bellingham is 93 (June 9, 1955), Hoquiam is at 90 (June 5, 2003 -- this one could survive; Hoquiam isn't looking quite as hot), Forks/Quillayute is at 92 (four times) and Paradise Ranger Station at Mt. Rainier is at 85, set June 1, 1986.

What about all time heat records?

  • Seattle: 103 (July 29, 2009)
  • Olympia: 104 (Twice: July 20, 2009 and Aug. 9, 1981)
  • Bellingham: 96 (July 29, 2009 -- sensing a pattern?)
  • Hoquiam: 95 (Aug. 19, 2016 and Aug. 10, 1981)
  • Forks: 99 (Aug. 9, 1981)


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