FastCast—Friday, Sep. 2 to Tuesday, Sep. 6:
After 2 days in the upper 80s, temperatures in Western Washington cooled on Thursday, with a thick marine layer keeping it cloudy through midday. Expect some morning clouds on Friday, Saturday, and Sunday as well, with clouds increasing on Sunday night and decreasing by midday Monday. Mostly sunny conditions will prevail on Tuesday. Highs will reach the low 80s on Friday, then the mid 70s on Saturday, then back to the upper 70s/near 80 on Sunday. Monday and Tuesday bring a drop back to the mid 70s. Overnight lows will be getting a bit cooler, dropping from the upper 50s Friday night to the low to mid 50s by Monday night. Eastern Washington will be dealing with unprecedented late summer heat, with Friday’s highs reaching the upper 90s to upper 100s. The Tri-Cities and Walla Walla areas have a chance to set all-time September records on Friday, with temperatures forecast in the 105-107° range. Highs in Eastern Washington will remain in the upper 80s to mid 90s through Tuesday. Additionally, the entire region will deal with smoke aloft from fires to the south. Eastern Washington may have degraded air quality (especially north of I-90 and in far Eastern WA) due to fires in the northern tier of WA and the northern Idaho Panhandle. Smoke aloft will move out of Western Washington by Saturday evening.
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Friday will likely bring unprecedented temperatures in Eastern Washington, with all-time September records possible in some locations. Western Washington will continue to be above average, but cooler than earlier this week.
Friday’s highs are below from the NAM model.
Notice the extreme highs in the mid to upper 100s in the lower Columbia Basin. Other parts of Eastern Washington will reach the upper 90s to low 100s. Western Washington will be much cooler, in the upper 70s to low 80s, potentially in the mid 80s in the foothills and near Olympia. Areas on the coast will be nearly 40-45 degrees cooler than parts of Eastern Washington…an incredible difference within the same state!
To verify that these extreme temperatures will occur in Eastern Washington, let’s check the NAM forecast with the HRRR, another high-resolution forecast model.
The HRRR agrees with the NAM, showing extreme highs in the mid 100s in the lower Columbia Basin, and similar highs in the upper 90s to low 100s around Eastern WA.
Both forecasts suggest some all-time September records may be broken, most likely Pasco (record 101°), Walla Walla (record 104°), and Yakima (record 100°). The Pasco record may be broken by 5 degrees, an incredible feat.
Additionally, smoke will be present around the region. For Western Washington, it will be aloft, creating a hazy sky. The HRRR forecast for Friday afternoon is below, showing smoke aloft over the entirety of Washington state.
This is a heavier concentration of smoke aloft than in previous days, so expect a smokier sky and redder tint to the sun, especially at sunset.
This smoke will begin moving out of the region on Saturday, as seen in the Saturday afternoon forecast.
Most of the smoke aloft is coming from wildfires in Southern Oregon and Northern California. To understand the smoke situation better, the InciWeb wildfire updates map is below.
Notice the large concentration of fires in the Idaho Panhandle and the scattered smaller fires in the Washington Cascades. Those fires will be bringing surface smoke, heavy in places, to parts of Eastern Washington on Friday and overnight into Saturday morning.
The surface smoke forecast for Friday afternoon shows moderate to heavy surface smoke, especially closer to the Idaho border. Expect degraded air quality in any areas with dark gray, green, yellow, orange, and red colors. Even parts of Western Washington may deal with very slight surface smoke on Friday, but this will cease being an issue by Saturday morning.
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