Wednesday, January 23, 2013

Inversion Snippets

There's much to talk about today.  We'll do this rapid-fire style.

• As discussed in the previous post from last night, the inversion is now at its maximum strength.  In this morning's upper-air sounding from the Salt Lake City airport, the temperature increased from -15.5ºC (4.1ºF) at the surface to 7.6ºC (45.7ºF) at 2130 m (6988 ft).  Within the large-scale inversion, which is elevated just a bit above the valley floor, the temperature increases from -12.7ºC (9.1ºF) at 1623 m (5325 ft) to 7.6ºC (45.7ºF) at 2130 m (6988 ft).  The loop below shows the lowering and strengthening inversion over the past 8 mornings, concluding with today.  

• With the inversion lowering, higher elevations on the east bench are getting tantalizingly close to clean air.  

• Overnight low at the Salt Lake City airport 4ºF. Overnight low on Mt. Baldy (11,000 ft) 34ºF.  

• The 24-hour average PM2.5 peaked overnight at 127.8 ug/m3 in North Provo.  That is almost 4 times the National Ambient Air Quality Standard.

Source: Utah Division of Air Quality
• Hourly PM2.5 at the Salt Lake site continues to show massive variations with a peak in the afternoon.  The 24-hour average PM2.5 has declined from a peak a few days ago.  I'm not really sure if I buy this as representative of the long-term air quality trend along the valley floor.

 • Although there are more sensors collecting data for retrospective analysis, we have a desperate need for more real-time air quality sensors along the Wasatch Front.  We have access to only one sensor in each county.  For comparison, the Puget Sound Clean Air Agency provides hourly real-time data from 16 sites, including 8 in the Seattle area.   Here's a wild idea.  Put samplers on every Trax train and we can paint out the spatial structure of PM2.5 along and across the Salt Lake Valley at regular intervals.  Such sampling wouldn't be complete, but it would be a major step forward in knowing the quality of the air we breath in real time.  

• Not much change in the forecast through Friday.  A weak trough moves through tomorrow and should give us a stirring and weaken the inversion by warming the low levels and cooling the air aloft.  I still think it won't fully mix out the gunk.  Looks like some wet snow for both the mountains and the valleys.  

• A series of brush by systems followed by a stronger trough will probably bring an eventual end to the pollution by early next week.  It will be interesting to see what happens to PM2.5 levels over the next few days.  


  1. Just drove up Traverse Ridge Road. The inversion top is at 5400 feet. Temp rose from 19F at that elevation to 36F at 5500 ft and 43F at 5700 ft. That includes adjustment time for thermometer as I was driving... so basically 20 degrees F of inversion in about 100 feet elevation.

  2. Update... I managed to stop on the way down and check things out a little closer. It turns out, there was no inverted "layer" there... the change was instantaneous. The temperature literally varied over 20 degrees, between about 19 and 43F, from one side of the road to the other at one spot (although the exact place where it changes is sort of a moving target). In fact you could see what looked like "heat waves" in the air... light refraction due to temp difference. Its worth going to check out, I have never seen anything like it. Hard to find a good spot to stop along that road, though.

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