Much More Pessimistic Air Quality Outlook and Model Problems


Things are looking far more pessimistic this morning, with considerably less improvement in western WA and OR air quality than expected yesterday.

And these problems are highlighting issues with our modeling systems and ability to observe/simulation smoke in the lower atmosphere.   Paradoxically, such problems are what modelers like me live for, providing opportunities to learn and improve our systems.

Air quality has not improved overnight, as shown by the summary at 4 AM this morning from the excellent Washington State Dept of Ecology WASMOKE site.  Hazardous air over Puget Sound, the Willamette Valley, and parts of Eastern WA.

The model forecasts yesterday (HRRRSMOKE, Washington State University’s AIRPACT SYSTEM, the USDA Forecast Service GRAYSKY) were suggesting improvement by now….and it is not happening.   Even the experts at WA Department of Ecology were going for better conditions by this time.  

But surface air quality remains poor and at the very least is not improving as fast as the models suggested.   Last night I was worried about the forecast and couldn’t sleep well–and now that I see what is going on, I am going to give up on my pillow.    

I suspect I understand some of the problems and what they imply for the forecast.    But before I explain, let me note that forecasting smoke is very new technology and very difficult for several reasons.  And the current situation plays to several of our weaknesses.

Problem 1:   A cool, stable layer of smoke near the surface.

Air quality has improved greatly above roughly 5000 ft, as strong southwesterly winds have developed aloft.   Below that level, cold, smoky air is trapped by an inversion, a layer of the atmosphere in which temperature warms with height.   Think of the inversion as a barrier to atmospheric motions, a cap to the vertical movement of air.  It prevents the smoke from mixing out vertically. 

This situation is shown clearly by a plot of the balloon-launched radiosonde sounding at Forks, on the WA coast (see below).

Temperature is shown by the right-most solid line, dew point temperature by the left line. Height is in terms of pressure, with 700 being roughly 10,000 ft.  Wind are shown by the vectors/pennants to right (more little line, the stronger the wind).  

There is a cool, moist layer below roughly 5000 ft in which the winds are weak.  About roughly 5000 ft (840 to 820 in terms of pressure in hPa), you can see the inversion, above which the winds are much stronger and from the southwest.

The trouble is that the models are not accurately portraying the lower dead-air layer, bringing too strong winds below the inversion and mixing out the smoke more than reality.  Unfortunately, a classic problem with our forecast models, which we are struggling to fix.

And it is worse than that.  The smoke itself is strengthening the inversion by preventing solar radiation (and thus warming) from penetrating to the surface and by warming of the upper smoke layer by the sun.  Details we have to get right.

Just to impress you with the strength of the inversion, Sunday afternoon temperature were in the mid-50s in Portland, while in the mid-70s around Mt. Hood (see below, click to enlarge).

Problem 2:  Smoke over the Pacific

We are now getting onshore flow aloft (and to a lesser degree at the surface) and we are pulling smoke that was ejected during the past few days over the Pacific.  2-5 days ago, a huge amount was injected offshore (see image for Sept 11 below), and now some of that smoke is being pushed back in, and the models have an uncertain handle on its distribution.

The outlook this week

This week is good illustration why we need humans watching the automated systems.   It like a plane on autopilot that is about to crash into the mountain–we need to take over the controls.

The latest HRRRsmoke forecast is still improving the air quality too rapidly, particularly over western Washington and the coast (see forecast below for 3 PM).

Reality is shown by the plot of small particles at Beacon Hill in Seattle over the past 48h.  We are probably past the worst smoke concentrations and air quality is very slowly improving.  That is probably the story for the rest of today.  Slow improvement.  And it appears that this will be the story for Tuesday as well.  I just checked the latest National Weather Service forecast discussion–they appear to have the same take on the situation.  Sorry.

One Encouraging Note

Let me end with a positive.  Although air quality is not improving quickly, the decline in smoke above us yesterday  is resulting in more sunlight.  Below is the solar radiation at the UW for the past three days (Friday to Sunday).  Friday had some smoke, but solar radiation was not abysmally low (15.49).  The bottom dropped out on Saturday (4.28), worse than most dark, winter days.  But Sunday was a bit bitter (8.86) and hopefully it brightened your spirits.


My latest podcast:

Source link