The Perfect (Smoke) Storm and the Weekend Weather Forecast

Here in Seattle, the smoke was amazingly thick on Wednesday morning, only exceeded by the extreme event of Sept. 2020 and equaled by the smoky period in summer 2018 (see small particle levels at Lake Forest Park over the last 5 years ago).

The intense smoke was associated with a dying fire (Bolt Creek) in the Skykomish Valley.  

How could this be?

The explanation is found in my podcast (see below).  The "perfect storm" of meteorological conditions.

And talking of perfect, consider the weather conditions over the Northwest this weekend.

ANOTHER ridge of high pressure will develop over the West Coast this weekend (see upper level map , 500 hPa--about 18,000 ft late Sunday below).  And you know what that means.... warmth and sun.

But this time of the year we can't get really hot...so highs will only get into the upper 70s in the west.  Nearly perfect.  It won't last though...cooler temperates for mid-week, but little rain in the forecast.  My podcast goes into the details.

To listen to my podcast, use the link below or access it through your favorite podcast service.

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Air Quality Worsens Over Puget Sound this Morning

 I walked outside this morning in north Seattle around 6:45 AM and the smoke smell was very strong.   The expected worst (and last) day of the smoke is here and it is nasty.

The Seattle PanoCam this morning at sunrise clearly showed the shallow smoky miasma over the city.  Even the tops of some of the tall buildings are above the worst of it.  

 The calibrated Purple Air air quality sensors this morning shows the plume of terrible surface air quality exiting from the Skykomish Valley from the Bolt Creek fire, which then heads south over Seattle.   Purple colors indicate truly bad air quality.   Red is just bad.    The plume is relatively narrow...head east or west and you can get out of it.

The Puget Sound Clean Air Agency has a ceilometer in Marysville that shows the vertical structure of the smoke plume at that site (which is a bit north of the worst of it).  The graphic (shown below) shows that the worst of it (yellow colors) was down low and moved in last evening.  Yuk.

The latest high-resolution visible satellite image around 7:30 AM really shows the smoke from the Bolt Creek fire exiting the Skykomish Valley and spreading out over northwestern WA:

So what is going on and when will it stop?

The Bolt Creek fire is really not spreading but is smoldering in the interior.  This has gotten worse during the past few days as temperatures have risen and relative humidities have plummeted.   

Here is a plot of the relative humdity and moisture content of small dead fuels at the nearby Johnson Ridge RAWS site.  Yesterday, relative humidity dropped to around 10% and fuel moisture to roughly 6 %.

These are favorable conditions for fire.

The fire-favorable conditions have been driven by easterly (from the east) flow that unforunately pushes smoke into western Washington as well.

And the clear skies aloft and longer nights allow cooler/smoky air to settle into lower elevations and not mix vertically.   That is why conditions worse overnight.

But there is good news ahead.  Solar heating today should help mix the smoke through a larger volume of air reducing surface smoke concentrations.

Tonight, the pressure difference across the mountains will reverse, and cooler ocean air will move into the west.

Smoke time will be over for western Washington.  Unfortunately, that is not good news for the eastern slopes of the Cascades.

To illustrate, here are the near-surface smoke forecasts (from the NOAA HRRR smoke system) for this morning and tomorrow morning.  Good for Seattle, bad for Leavenworth.

So if you are sensitive to smoke and leave in Puget Sound.....wait a few hours before taking that walk or run.  If you are living in east Washington....you better get your exercise in today....