The End is in Sight: Stormy Weather Finally Arrives to Kick Out the Smoke

 FastCast—Wednesday, Oct. 19 to Saturday, Oct. 22:

Tuesday brought the full effect of the recently expanded wildfires to Western Washington. Air quality reached its worst levels yet for many in the Cascade Foothills and from I-90 northward, skyrocketing into the “very unhealthy” to “hazardous” categories. Wednesday will be another very smoky day, with air quality significantly degraded around the entire Puget Sound region and the Portland area. However, onshore flow will return on Thursday, with smoke-free skies west of the Cascades by Thursday evening. Highs on Wednesday and Thursday will reach the mid to upper 60s, with lows in the mid to upper 40s. Then, on Friday, the first storm of the season will arrive in Western Washington. Highs for the foreseeable future will plummet to the low to mid 50s, with lows in the low to mid 40s. The most significant rain since June will soak the region from Friday morning to midday Saturday, with 0.5-1.25 inches across Western Washington. Areas from Chehalis southward and in the mountains may pick up over 1.25 inches. Eastern Washington will get rain as well, with 0.25-0.75 inches expected, and 0.85-1.5 inches near Walla Walla and the Blue Mountains. With much colder temperatures, the snow level will plummet to 4,000 to 5,000 feet. 2-6 inches of snow are expected at Stevens and White Passes. Additionally, winds will be breezy, likely gusting 20-30 mph around the region (possibly stronger near the water). This system, along with those following it, will be the end of smoke in Western Washington and will begin extinguishing active wildfires. This is just the first system…active weather is expected through the end of October, so stay tuned!

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Continue reading the full blog below!

Tuesday was one of the smokiest days for many areas in Western Washington. This was due to the explosion in fire activity after the easterly winds this past weekend. Many areas had horrible air quality, with readings in the “very unhealthy” and “hazardous” categories (190-500+) in the Eastside, the Cascade Foothills & Valleys, Whatcom County, SW British Columbia, and the Portland/Vancouver metro area. 

Unfortunately, bad air quality will continue on Wednesday. Let’s take a look at the HRRR smoke forecast, starting at 7 AM Wednesday.

On Wednesday morning, heavy surface smoke will be present from Vancouver, BC to Salem, OR. Air quality will be unhealthy.

By 4 PM Wednesday, conditions will be marginally better.

Notice that smoke has gotten a tad bit lighter in the lowlands, but overall, Wednesday will be another day of significantly degraded air quality due to heavy surface smoke.

However, Wednesday will be the last day of bad smoke for Western Washington! Below is the forecast for 7 AM Thursday.

By Thursday morning, onshore flow has slowly began eroding the smoke west of the Cascades. For many areas in the foothills and from Seattle southward toward Portland, surface smoke will remain. Eastern Washington will be dealing with heavy surface smoke.

Improvement will be very noticeable by 5 PM Thursday. 

Western Washington is almost entirely clear of smoke, as well as Portland. However, Eastern Washington will continue to deal with surface smoke on Thursday. Air quality will improve to “good” in Western Washington, while “moderate” to “very unhealthy” air quality is expected for Eastern WA, especially in thick smoke downwind of fires.

The end of smoke impacting Western Washington is in sight. This is due to a major pattern change that will end the warm, dry, and stagnant conditions that have persisted for the past few months.

Below is the European model forecast for Wednesday.

On Wednesday, a massive high pressure ridge is dominating Western North America. This is keeping smoke in Western Washington.

However, by early Saturday, the pattern has done a 180!

By Saturday, a massive trough of low pressure is over the Pacific Northwest, breaking down the persistent ridging of the last few months.

So…what will this pattern change bring? Basically, this will be the first storm of the season, bringing significant rain, mountain snow, and much cooler temperatures.

Below is the European model forecast for rain from Friday morning to early Saturday morning.

Expect 0.7-1.25 inches of rain across Western Washington. The most rain (1.25-1.5”) will fall on the South WA Coast, in the Cascades, and south of Chehalis. Thankfully, Eastern Washington will get rain as well, with 0.25-0.75 inches expected, and 0.85-1.5 inches in the Blue Mountains and near Walla Walla.

This system will bring a large drop in temperatures that will last for the foreseeable future. Below is the European model forecast showing temperature change from 5 PM Thursday to 5 PM Friday.

From Thursday to Friday, lowland temperatures will drop 10-20 degrees! In Eastern Washington, temperatures will drop an incredible 20-30 degrees in 24 hours!

What will the highs be? Take a look at the European model forecast for Friday’s highs below. Expect similar temperatures for the remainder of October.

Highs in Western Washington and Oregon won’t get above 60º. Even Eastern Washington will only be in the mid 50s to low 60s.

Finally, with much cooler temperatures and an influx of precipitation, snow levels will plummet to 4,000-5,000 feet by Saturday, bringing the first snow of the season to Stevens and White Passes and ski areas at similar elevations. The European model snow forecast through early Saturday morning is below.

Expect 2-6 inches above 4,000-5,000 feet, with the most snow around Mount Rainier.

The combination of rain, snow, and a 20-30º decrease in temperatures will effectively extinguish wildfires in the Cascades. For most fires, it will take a few weather systems for them to be fully extinguished, but with more systems on the horizon, that won’t take long. We can say with reasonable confidence that after Thursday, Western Washington is done with wildfire smoke!

Stay tuned for more updates later this week!