I have gotten several messages about yesterday's localized smoke event, so let me answer them here.
First, the smoke concentration in some locations north of Seattle was the greatest in many years.
For example, at Lake Forecast Park, values surged to over 300 micrograms per cubic meter for a short period at the surface (see plot below).
This is extraordinarily unhealthy air. Fortunately, particulate levels subsequently declined rapidly in the evening as the plume of smoke moved northward.
Several people asked: Why were the smoke levels lower to the southeast--closer to the fire? This is illustrated by the particle concentration map below near the height of the episode. Red and purple are high values.
Air quality was much better in the mountains than in the lowlands!
To see what happened, let's examine how the smoke evolved aloft, using the laser ceilometer run by Puget Sound Clean Air Agency on Beacon Hill of south Seattle (below). Time is on the x-axis and height in meters on the Y-axis. Keep in mind that 3000 meters is roughly 10,000 ft. Red and yellow indicate either clouds or relatively dense smoke.
There were some low-level clouds between 6 and 9 AM (red color), which dissipated by around 10 AM. But then smoke started coming in aloft around 11 AM (at about 800 meters above the surface).
The smoke mixed down to the surface around 5-6 PM and started to lift later in the evening. This led to the rapid and profound air quality degradation.
This morning, air quality was significantly improved over western Washington, but poor air quality still persists east of the Cascades.
As I will discuss in my next blog, we have made the transition to a fall-like pattern and regional temperatures should be MUCH cooler during the next few weeks. Wildfires should decline.
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