Friday, January 25, 2013

Mother Nature's Final Insult

A friend described yesterday's freezing rain as the 7th plague.  I'm not sure what the other six are, but I suppose we could include split flow, inversion, and pollution.  Today we can add fog.  We might have to add drought if this pattern continues.  Feel free to comment with your additions.

By Utah standards, there is a remarkable rain crust on the snow here in the Salt Lake Valley.  It leaves a  shimmer on the snow and is several millimeters thick.

Crusts of this type, sometimes far stouter, are not uncommon where I grew up in upstate NY. I swear I still have bruised shins from trying to walk, snowshoe, and ski on days like this.  I had a far lower tolerance for bad snow then than I do now.

It may be foggy and not look too polluted, but an inversion remains in place and a quick look at the real-time charts from the Utah Division of Air Quality shows that Salt Lake, Utah, Weber, Uinta, Tooele, Cache, and Box Elder counties remain above the National Ambient Air Quality Standard for 24-hour average PM2.5.  Most remarkable is that despite yesterday's freezing rain, the PM2.5 concentrations (24-h average) have actually gotten worse at a few sites, including Salt Lake City.

Source: Utah Division of Air Quality
On the other hand, the air quality has thankfully improved in Provo, although the PM2.5 levels are still high.  

Source: Utah Division of Air Quality
Contrasts in the long-term trends and daily variations of PM2.5 at these sites during this event remain unexplained.  My knowledge of emissions, aerosol physics, and atmospheric chemistry is insufficient to provide a good explanation.  Perhaps others can pipe in.  

Mother Nature has at least one final insult.  This weekend, she will probably keep us locked into crappy air.  A storm passes to the south, and one approaches from the northwest, but doesn't make it into Utah by late Saturday afternoon.  As a result, Salt Lake and Utah Counties are in a dry slot between these two storms when one looks at the total accumulated precipitation through 5 PM MST Sunday.  

Source: NCEP
This means we'll probably remain inverted and polluted through the weekend.  There's some hope for Sunday night and Monday, but the models are still showing some spread in the intensity and track of the approaching trough.  It looks like we'll get at least a partial mix out, and probably a full mix out, but we'll have to see how things come together.  

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