Significant Heat Wave Ahead for the Pacific Northwest

FastCast—Saturday, Aug. 12 to Tuesday, Aug. 15:

A heat wave is likely for the Pacific Northwest next week. Temperatures will likely reach their hottest levels of 2023 across the region. In the lowlands, expect temperatures to start climbing on Saturday, with highs in the upper 70s to low 80s. Morning clouds will gradually clear through the day. The temperature climb continues on Sunday, with lowland highs increasing to the mid 80s, with some areas reaching the upper 80s to low 90s, mainly in the foothills and from Olympia westward. Monday will be hotter still, with highs in the upper 80s to low 90s. Isolated locations will reach the mid 90s. Tuesday currently looks to be the hottest day in the lowlands, with highs in the low 90s. Low temperatures will be on the warm side, likely in the low to mid 60s, warmest from Monday morning onward, especially in urban areas. Of note, areas from Everett northward will likely peak in the low to mid 80s. Keep reading the blog below to see even hotter temperatures expected for other ares of the Northwest.

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Continue reading the full blog below!

A heat wave is ahead for the Northwest, with the hottest temperatures of 2023 expected. 

Let’s start with the European model forecast for the next few days. First, the forecast for Saturday.

On Saturday, expect lowland highs in the upper 70s to low 80s. Eastern Washington will reach the upper 80s to mid 90s, and the Willamette Valley will reach the upper 80s. The coast will reach the upper 60s to low 70s.

Temperatures continue to climb on Sunday, as seen in the European model forecast.

Sunday’s highs in the lowlands will reach the mid 80s, with the Kitsap Peninsula and areas from Olympia to Shelton and southward in the upper 80s to low 90s. The Willamette Valley will skyrocket to the upper 90s to low 100s, hazardous temperatures to the population. Eastern Washington will reach the low 90s to low 100s, and the coast will reach the upper 60s to mid 80s, hottest inland.

Monday will be even hotter across the region, as seen below.

Monday’s highs in the lowlands will be in the mid 80s to low 90s, except in the mid to upper 90s from Shelton southward. The Willamette Valley will reach the low to mid 100s, and Eastern Washington will reach the mid 90s to mid 100s. The coast will reach the low to mid 70s on the beaches and the mid 80s to low 90s inland. 

Tuesday looks hotter for the lowlands and Eastern Washington, but stay tuned as that forecast is still uncertain.

Low temperatures will be on the warm side, which will be difficult with prolonged heat. Below is the forecast for lows on Monday morning.

Lows by Monday morning will only drop to the mid to upper 60s in the lowlands, the upper 60s to low 70s in the Willamette Valley, and the mid 60s to low 70s in Eastern Washington.

So, what is causing this prolonged heat wave? It is a large high pressure ridge dominating the weather pattern across the Pacific Ocean, as seen below on the European model.

Notice the ridge in the black box. It is centered offshore of the Pacific Northwest, and its location is what determines the temperatures. If the ridge sets up further east (closer to the PNW), temperatures will be hotter. Overall, this ridge means extended hot and dry conditions (all next week).

There are a few things I would like to highlight with this heat wave potential. First, the potential for historic heat in the Willamette Valley, as seen in the European model forecast for Portland (below).

This forecast shows 3 consecutive days of highs over 100º in Portland, from Sunday to Tuesday. Exacerbating the heat will be low temperatures in the mid 60s to low 70s.

Second, while this heat is not record-breaking or unprecedented for Eastern Washington, it will still be dangerous. Below is the forecast for Tri Cities Airport in Pasco.

Notice that from Sunday to Friday, highs in Pasco are over 100º, with a peak of 112º on Tuesday and a total of 4 days over 105º. 

Finally, the forecast for Seattle (SeaTac Airport), seen below.

Notice that Seattle’s highs are significantly lower than Portland, due to the influence of Puget Sound. Despite lower high temperatures, notice the lows in the low to mid 60s all next week, on the warm side for the metro area.

However, highs in other parts of the metro area, mainly south and east of Seattle and on the Kitsap Peninsula, will likely be hotter than this, as seen in the forecast below for Olympia.

Notice how in Olympia, there are 4 days over 90º, with a potential for a fifth day on Sunday. Lows in Olympia will be warmer, likely up to the mid 60s during the hottest days.

Stay tuned to the blog for additional updates as this heat wave approaches and the forecast gets more refined!