This is a brief morning update to reflect the slower nature of the smoke clearing out of the Puget Sound area.
Below is the situation at 8 AM Thursday, from the HRRR smoke model.
Smoke is still engrained across most of Western Washington and most of Western Oregon.
AQI levels at 7:45 AM Thursday are relatively similar to Wednesday night, as seen in the Purple Air map below.
The reason that smoke is clearing slower than expected is due to a strong inversion. This inversion is what kept very unhealthy to hazardous air quality in place overnight.
Inversions keep out “mixing” of air, which keeps low level air fresh. As onshore flow begins Thursday, it will slowly erode the inversion that is in place over the lowlands, and the Central Sound (entire metro area) will be the last area to clear out.
Let’s time this out. 12 PM Thursday is below.
Notice that smoke is improving in the mountains, with plumes of smoke starting to move east. Surface smoke is still moderate to heavy in the Puget Sound area and Willamette Valley.
By 4 PM Thursday, there is further improvement.
Smoke has been pushed back to only cover areas between Olympia and Mount Vernon. Eastern Washington is dealing with bad AQI due to westerly flow.
At 8 PM Thursday, onshore flow has eroded smoke coverage significantly.
By nightfall, smoke will have mostly cleared from areas between Olympia and Tacoma, now only extending from Federal Way to Skagit County. Eastern Washington will be dealing with dense surface smoke from long plumes coming off fires in the Cascades.
The final image is for 12 AM Friday.
At this point, rain will be on our doorstep. At midnight, the lowlands are almost entirely clear of smoke, as well as the Willamette Valley. Conditions will remain poor overnight in Eastern Washington.
Overall, due to the inversion, it will take over 12 hours for smoke to totally clear out of Western Washington. However, by Friday, expect “good” air quality and our first significant rain since June! More on that tonight…
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