September 21, 2022

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 better get your exercise in today....


  1. Thank you for focusing on this topic. There is a glaring shortfall in sophistication of air quality analysis, forecasting and reporting here in the western states. I am so thankful for access to such great data- especially purple air. I use the data to plan my time outdoors especially any exertion or prolonged time. This information is so much more important than air temperature, yet most people are unaware or unsophisticated about 2.5u pm. This is a real space for leadership.

    1. The Canadians have a pretty good forecasting tool which, fortunately, includes the U.S.

  2. Really terrible air in Bothell for my bike ride to work this morning. I repeat: What do the models say about the arrival of the first storm (not just a little drizzle)?

  3. Yes, agreed with Isaac - the public remains in the dark concerning air pollution of all types, and their health/benefit of remaining indoors if at all possible, versus out. I use Purple Air REGULARLY, but they are a data center, not a forecasting center. Purple Air lacks ground level WIND speeds and direction, or I could forecast for myself.

    In any event, had closed up the house (uninsulated/no a/c etc) when heading to bed, left Austin Airs on med/low settings on main floor, and headed to basement bedroom, where I cracked a few windows and the door and slept beginning 11p. I nose breath, thank heavens.

    At 6:30 AM or so, here on Fremont hill, I was awakened by Acrid air/smell.

    Being an 'aware' sort, I lay in bed a bit thinking of my options, and knowing I needed to grab my quilt and head up to the Austin Air'd/closed windows living room (couch). Oddly for me I was able to get back to sleep until nine : )

    This is simply the telling of the tale that, at least for me, our mammalian senses actually work to protect us. Would love to hear from others who were awakened prematurely by the dark PURPLE AIR this AM - as it was indeed a harsh plume, and so it remains now (red to purple to nearly black in North Seattle/King County).

    I also wonder why I am hearing the adorable children at BF DAY Elementary out there in the playground. It would seem that recess might be indoors today in the cafeteria, ideally with high test hvac running filtered air the entire time.

    Not rocket science, but the public at large seems clueless.

    Thanks Cliff for your post! It's always nice to have a few more facts. AND I certainly hope your prediction of 'clearing from the West' by tomorrow comes to pass. Your last prediction for air clearance took about 4 - 5 days beyond your (rather optimistic) statements at the time.

    We just need better Smoke Forecasting for this country/the forested West in particular (and it should include CA and MX of course) . . . 'Climate Change' has happened/is happening, and we need to know how to act from day to day, along with how to plan or futures.

    If Seattle weren't so dysfunctional and cared more about quality of life, our community centers would ALL have sunny gathering spaces with smoke/virus cleared air, via high-functioning HVAC systems that run especially diligently when heat/smoke/covid, etc require it to create, yes, safe and happy places to convene, and dare I say 'play'!

    Thanks again for all.

  4. @eugenie cullen, I've found that flipping between the PurpleAir map and the map can be a pretty good amateur guide to when the air quality will change. But I'm in total agreement that this ought to be a bigger part of public policy.

    1. the PurpleAir data is available as an overlay on Windy. Click on "more layers" in the observations section (bottom right), not the model layer section (right side panel) and then select Air Quality Stations. You can then have the model layer on winds and voila!

  5. Thank you for the explanation, and prognostication for a clearer (air) future, Professor! man, it was as bad today in view ridge as i've ever seen it or smelled it.

  6. I think Tacoma missed the bulk of this as it was never bad here yesterday (too far south) and the last time we had it bad was what, a couple of weeks ago where one day, it was sepia toned for much of the day.

    Today, it's pleasant, with the sun in/out of the spotty clouds and a light breeze and clear.

    As to others saying we need more info/forecasting about air quality and how many seem clueless. I think there is some aspects that are true, but you can give then the info, but will they pay attention? Not as likely, as the old saying goes, you can lead a horse to water, but you can't always get him to drink it, or something like that.


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