Sunday, January 11, 2015

The Curse of the Weak Trough

Fog, smog, and dreary skies over the Salt Lake Valley this morning
Yesterday and today residents of the Salt Lake Valley and Wasatch Front have experienced the curse of the weak upper-level trough passage.

When an inversion is in place, a strong upper-level trough passage can blow out the pollution, improve the air quality, and usher in clearer skies.  On the other hand, a weak trough passage just gives us a blanket of dreary mid and upper-level clouds and just enough precipitation to moisten up the low levels and increase the fog coverage.

That's just what has happened over the past 24 hours, and we're left not only with fog and dreary skies, but also plenty of pollution as PM2.5 levels have been highly elevated and well above National Ambient Air Quality Standards.
Source: Utah Division of Air Quality
We are probably stuck with this damp, polluted airmass until at least tomorrow when another weak, but somewhat stronger trough moves into northern Utah.  This one should bring more precipitation, stronger flow, and colder air aloft.  It has more potential to bust the lid and clean things out.  I'm not going to guarantee a full mixout, but I think it's more likely than not that this one will do it.  I'm more enthused about this one than yesterday's.  It will also bring some badly needed snow to the mountains (we did get 2-3" last night...not much, but a start).

Park City Readers:

If you are looking to buy Secrets of the Greatest Snow on Earth at a local retailer, I signed three copies for retail sale at Jans yesterday (1600 Park Avenue).  Get them while they last.  Dolly's Bookstore should also have some in stock soon, so give them a call and put it on reserve.

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