Tmax — Seattle's Past and Present Weather and Climate in Charts and Graphics

This summer has been pretty nice in Seattle. Aside from a few very extreme temperature days in late June, it has been a pretty typical summer. Aside from the three days in late June which exceeded 100˚F, about five (5) other days reached 90˚F, so far. The summer is not over yet. Nevertheless five days exceeds the annual average at Seattle-Tacoma International Airport (KSEA) average of about 3.3 days per year reaching 90F or higher. And adding back in the 100˚F days in late June, means we’ve had eight (8) days this summer at 90F or above, more than twice the number of hot days we see in summer. Since 2014, this seems to be the new norm though we’ve had one year since then where we reached 90˚F only twice.

Figure 1 below shows the number of days each year where the maximum daily temperature reached 90˚F or higher at Seattle-Tacoma International Airport. Click on the chart to expand it.

Figure 1. Counts of 90˚F Days. Click to expand. — Figure 1. Counts of 90˚F Days.
*Click to expand.*

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Charts updated: August 14, 2021, 8:00 AM PDT

We’re in the midst of a second heat wave this summer. Our first, in late June, was a scorcher, setting an all time high record for Seattle at Seattle-Tacoma International Airport (SeaTac) on June 28 of 108˚F. We had three days of temperatures greater than 100˚F in that period.

This week’s heat wave (and now smoke wave) isn’t quite as hot. But temperatures are back above 90˚F. This is a arbitrary threshold, but it is as good as a threshold for a heat wave as any, so we’ll use it.

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So, how often does it get to 90˚F or greater in Seattle, The Land of No Air-Conditioning? It is pretty much a summer only phenomena and is not as uncommon as one might think. Figure 1 shows maximum daily temperatures at SeaTac going back to January 1, 1949. Most summers record at least one or more days of 90˚F, but not all. This year is about average. We’re not through with this current heat wave, so one can expect to see another red dot for today and probably tomorrow. I can’t predict beyond tomorrow whether we will see anymore really hot days. But it is becoming late summer. Days are gradually getting shorter and nights longer and we only have about 2-½ more weeks until September begins.

Ironically, in the six or so weeks between this summer’s heat waves, we’ve had one of the most pleasant, if a bit dry, summers in my 38 years here.

Click on Figure 1 to expand it. I’ll update it over the next few days as this heat wave plays itself out.

Figure 2 was added on August 14. It shows a zoom-in of Figure 1 for the last 10 years. Most summers in Seattle experience at least a few days with temperatures reaching 90˚F.

Figure 2 also shows the extraordinary heat wave Seattle experienced in June 2021 where temperatures exceeded 100˚F for three straight days.

Tags: Tmax, maximum temperatures, weather, Seattle-Tacoma International Airport, KSEA, summer, heat

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