I walked out this morning north of Seattle around 6:45 a.m. and the smell of smoke was strong. The expected (and final) worst day of smoke is here and it’s horrible.
PanoCam Seattle this morning at sunrise clearly showed a thick haze of dust covering the city. Even the top of some tall buildings is above the worst part of it.
Calibrated Purple Air air quality sensors this morning showed terrible surface air quality escaping from the Skykomish Valley from the Bolt Creek fire, then heading south through Seattle. Purple indicates really bad air quality. Red is just bad. The tuft is relatively narrow… go east or west and you can get out of it.
The Puget Sound Clean Air Authority has an altimeter in Marysville that shows the vertical structure of the chimney at that site (slightly north of its worst). The graphic (shown below) shows its worst (in yellow) having gone low and moving last night. Yuk.
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The latest high-resolution visible satellite image at around 7:30 a.m. actually shows smoke from the Bolt Creek fire escaping into the Skykomish Valley and spreading out into northwest WA:
So what is going on and when will it stop?
The Bolt Creek Fire is actually not spreading but smoldering inside. This was received worse over the past few days as temperatures rise and relative humidity plummets.
Here is a chart of the relative humidity and humidity of small dead fuels at the nearby Johnson Ridge RAWS site. Yesterday, relative humidity dropped to about 10% and fuel humidity to about 6%.
These are favorable conditions for fire to occur.
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Favorable conditions for firefighting were facilitated by easterly (from the east) runoff that mercilessly drifted into western Washington.
And clear blue skies overhead and longer nights allow cooler/smoky air to settle at lower altitudes and not mix vertically. That’s why the condition got worse overnight.
But there’s good news ahead. Today’s solar heating systems will help to mix the smoke through a larger air volume reducing the smoke concentration on the surface.
Tonight, the pressure differential over the mountains will reverse and cooler sea air will move westward.
The time of smoke and fire will end in western Washington. Unfortunately, that’s not good news for the eastern slopes of the Cascades.
To illustrate, here’s the near-surface smoke forecast (from the NOAA HRRR smoke system) for this morning and tomorrow morning. Good for Seattle, bad for Leavenworth.
