Wednesday, January 9, 2013

Good Riddance to the Inversion

Overnight, 24-hour average PM2.5 values at the Utah Division of Air Quality site in Salt Lake City reached their maximum for this event, just over 73 ug/m3.

Today is a day to keep an eye to the sky as it will be very interesting to see what happens to the valley cold pool (a.k.a. inversion) this afternoon.  Winds aloft are presently fairly weak, but are expected to increase dramatically during the day.  By late this afternoon, the 700-mb (crest-level) flow is forecast to be about 40 or 45 knots over Salt Lake City.

Can the valley cold pool withstand this sort of onslaught of strong flow aloft?  Will the benches scour out while a thin lens of cold air and pollution remains on the valley floor?  Time will tell.  Our models struggle with cold-pool erosion, so these are the days that I watch and learn.

In any event, the cold pool won't last long as a cold front will move in on Thursday, bringing some freshies for the mountains and the valleys.  I may have to do a tour in the Avenues foothills on Friday if the front comes through.

The air behind the front is extremely cold, with 700-mb (crest-level) temperatures dropping below -18ºC on Friday.

I suspect that's the coldest air of the season.  Bundle up good if you are skiing Friday or Saturday.  Temperatures are likely to be below 0ºF in the higher elevations.


  1. Three cheers for the inversion scour! Now to figure out how many layers to put on my four year old for his first ski lesson on Sunday...

  2. I was shocked this morning to see the mountains from my window in the avenues. Then, I checked one of the air quality websites and noticed that PM2.5 was down to 25.1 ug/m3. Obviously, it's not a complete clearing, but it seems we have randomly received some relief. But I cannot figure out why. Can you?

    1. It is not uncommon for PM2.5 to fluctuate on short time scales. These fluctuations aren't always meteorological - they can be related to emissions and chemistry. The Salt Lake site dropped to 25.1 ug/m3 this morning, but went back up over 60 a few hours later. This happened a couple of days ago as well.

      Things do appear to be scouring out on the benches now. At about 3:30 it is about 41ºF here at the U and 33ºF at the Salt Lake airport. I suspect PM will be dropping everwhere, but it has probably dropped the most on the benches.