Monday, December 17, 2018

A Dirty, Stinky Lake Breeze

It was nice to walk to the bus early this morning, enjoy the mild temperatures, and breath clean air.  For a while, south winds ahead of an approaching upper-level trough had pushed back the valley cold pool to the north valley and over the Great Salt Lake.  The transition was especially strong at the Neil Armstrong Academy where around 6 AM MST the winds increased to over 10 knots with a SSE component.

Source: MesoWest 
At the same time, the temperature rose dramatically, from 27ºF to 46ºF. 

Source: MesoWest
However, a look at the two traces above shows that the wind eventually flopped around again to NW and the temperature dropped all the way down to 34ºF.

Further, the PM2.5 concentrations dropped to near zero with the temperature rise, but then crept back up to 35 ug/m3 with the shift to NW flow, although they have dropped back down to 20 ug/m3 at the moment.  

Source: MesoWest
The mesowest station plot for 1718 UTC (1018 MST) shows the situation really well.  In the southern part of the Salt Lake Valley, the flow is southerly and temperatures are in the 40s.  In the northern half, there is northwesterly flow with temperatures in the 30s. 

Source: MesoWest
Sadly, that cold, stable, polluted air has pushed its way back to the south.  This is not uncommon.  The air over the relatively cold Great Salt Lake in a situation like this is the densest, stingiest, and hardest to remove.  Right now there is a battle between the larger-scale southerly flow and the lake breeze which wants to push that cold air southward. 

The air quality where you are today is dependent on who wins that battle.

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