Wednesday, January 16, 2013

Inversion Intricacies

We've been fortunate thus far with the early stages of this inversion event.  The ridge has pushed eastward just a little slower than expected, so the rise in temperatures aloft hasn't been as rapid as thought, and abundant mid-level clouds have helped to warm the valley.  Nevertheless, temperatures have climbed more aloft than in the valley, as can be seen in the Mt. Baldy and Salt Lake time series below.

Source: MesoWest
The morning sounding shows a primary inversion based at about 772 mb (7800 ft).  Within the inversion, temperatures increase from -13.3ºC at the base to -4.7ºC at the top.  Below the inversion I've identified the valley cold pool, which is about 3500 feet deep, although there is a weaker, secondary inversion within the cold pool.

Skew-T Source: NCAR/RAL
The good news is that the primary inversion is still fairly high so that we are getting some vertical mixing of pollutants.  This has helped keep PM2.5 levels below the 24-hour NAAQS thus far in the Salt Lake Valley.

Source: Utah DAQ
More elevated levels are found to the north in Weber and Cache County, with the latter eclipsing the 24-hour NAAQS overnight.  

Source: Utah DAQ
Model forecasts indicate strengthening and lowering of the inversion today and tonight, with little hope of a major breakout through at least the weekend and possibly early next week.  Bummer.

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