No FastCast tonight…keep reading below for an update on the fire weather conditions impacting Western Washington.
Weak winds and light offshore flow kept heavy surface smoke stuck in the lowlands most of Saturday, with air quality staying steady at unhealthy levels of 140-200, in the “unhealthy for all” and “very unhealthy” categories.
On Saturday evening, offshore flow increased. Winds are gusting 30-35 mph in towns like Enumclaw and North Bend. Downstream of gaps, in areas such as Kent, Maple Valley, Snoqualmie, and Issaquah, temperatures are in the mid to upper 70s at 10 PM! Humidity downstream of the gaps is in the 20-35% range, versus 75-95% in sheltered areas. Temperatures are also 10-20º cooler in sheltered areas.
Due to gap winds, overnight lows will only be in the mid to upper 60s if your location is exposed to the gap winds. For sheltered areas, lows will drop to the mid 50s, still warm for October. Check current temperatures here (NWS Map).
Record-breaking temperatures are expected across most of the lowlands on Sunday. The HRRR forecast is below, showing temperatures at 3 PM Sunday.
The HRRR shows hot temperatures, with highs in the lowlands reaching the mid to upper 80s due to dry offshore flow. These temperatures are flirting with all-time records for October. Eastern Washington will reach the upper 70s to low 80s, the Willamette Valley/SW WA will be in the upper 70s to mid 80s, and the coast will be cool, in the upper 50s to low 60s.
The NAM forecast is a bit more reasonable, showing Sunday’s highs below.
The NAM shows highs in the lowlands reaching the upper 70s to mid 80s. This is still extraordinary, but a bit more reasonable than the HRRR. Most of the remainder of the map remains the same.
Expect very dry conditions on Sunday as well, with relative humidity values in the 20-35% range around Western Washington. Additionally, gap winds will gust 25-35 mph in foothill communities and up to 30-45 mph in the mountains through Sunday morning.
Now for the smoke forecast…despite a very smoky Saturday, the smoke won’t linger for weeks like it has recently. Onshore flow will return by Sunday night, significantly lessening smoke coverage. Let’s time it out below.
We will use the HRRR smoke model, starting at 5 AM Sunday.
Surface smoke will be present across Western Washington, heaviest along the Strait and in Whatcom, San Juan, and Skagit Counties, due to SE winds. Heavy surface smoke will be present in a large portion of Central Washington.
By 12 PM Sunday, smoke plumes from individual fires will be getting more defined.
Surface smoke will still be stuck in the lowlands, aided by smaller areas of thick smoke due to fires in the Cascades.
By 5 PM Sunday, improvement can be seen along the coast.
At this point, smoke plumes from local fires will be at their peak, after a full day of strong offshore flow. Winds will have shifted to bring the heaviest smoke straight into Whatcom, Skagit, and San Juan Counties, plus SW British Columbia. Surface smoke will still be stuck in the lowlands, as well.
More improvement is expected by 8 AM Monday.
On Monday morning, surface smoke will be most noticeable from Olympia northward, especially close to the Cascades. Of note is that while onshore flow will push smoke out of the lowlands, a new fire in Oregon’s Coast Range will pump surface smoke into the Portland, Vancouver, and Kelso/Longview metro areas. Lots of surface smoke is still expected in Eastern Washington.
By 5 PM Monday, conditions in the lowlands will have improved even more.
Smoke plumes from fires in the Cascades will bring areas of bad air quality to Eastern Washington and the Cascades, but by Monday evening, surface smoke will be making its way out of the lowlands (though the same can’t be said for Portland and SW WA).
Another big change on Monday will be dramatically cooler temperatures, as seen in the 24 hour temperature difference forecast from the NAM model. This shows the difference in temperature between 3 PM Sunday and 3 PM Monday
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