Excessive heat is ahead for the Pacific Northwest. As of Sunday evening, at least 3 days above 90 degrees are expected, and Excessive Heat Watches have already been issued. High temperatures of 90-100 degrees are likely for Western Washington. (Below: surface temperature forecast from the UW model for 5 PM Friday).
As with any forecast more than approximately 5 days out, some uncertainty is to be expected. To illustrate that, below are 3 informative graphics from NWS Seattle showing the spread in forecast highs and the average. These graphics are for Thursday, Friday, and Saturday.
Overall, temperatures will be hottest from Seattle southward and away from the water, as usual.
In accordance with this forecast, NWS Seattle has issued an Excessive Heat Watch, in effect from 12 PM Wednesday to 11 PM Saturday. The alert is below.
The top of the alert details what temperatures to expect for the area. This heat wave will be about 5-10 degrees cooler than the heat wave in late June. While this heat wave will be a bit cooler than June, a few locations will reach 100+ degrees, mainly in the South Sound (97-101), Chehalis Valley (97-101), Willamette Valley (100-107), valleys of the Cascade foothills (96-102), and east of the Cascades (102-112).
Another aspect of this heat wave, as with the last one, will be warm nighttime temperatures. In the Weather Underground forecast for Federal Way below, you can see low temperatures only dropping to the mid 60s from Wednesday night to Saturday night.
Temperatures will gradually warm up, from the upper 70s/low 80s on Monday to the upper 80s (possibly low 90s) by Wednesday. Thursday, Friday, and Saturday will be the hottest days, with temperatures well into 90s.
There is one caveat: smoke. Some extended forecasts have suggested that both smoke aloft and surface smoke could be present during the hottest days, due to low level offshore flow and upper level southerly flow. Smoke would definitely have a dampening effect on high temperatures, but it is too early to determine what will happen, so stay tuned.
Speaking of smoke, northwesterly flow aloft will bring light concentrations of upper air smoke to our skies from fires in Canada and Alaska. This will just be a light haze and less hazy than our last round of smoky skies. The forecast for 7 AM Monday is below.
Slightly heavier concentrations will be over parts of Oregon, but again, much less hazy than last week’s smoke.
Let’s end on a good note…this was a refreshing weekend across the state! Many locations ended their dry streaks, as weak systems brought rain and cooler temperatures to most of the region. 3 day rain totals ending 9 PM Sunday are below.
Generally, the rain forecasts verified well. The coast, mountains, and areas north of Seattle got the most rain, as expected. Rain-shadowed areas from Seattle to Olympia got less. Worth noting is the 0.7-2.4 inches of rain in the mountains and 0.03-0.2 inches in the fire-weary Methow Valley. Any rain will help to limit fire danger, though upcoming dry conditions will heighten fire danger once again.
Stay tuned for updates on the upcoming heat and make sure to take heat precautions!
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