Monday, December 12, 2011

Subtle Changes for the Better (for Some)

Yesterday, smog enveloped the east bench and Avenues foothills to an elevation of at least 5000 feet.  The top of the smog layer was not especially well defined, but if you made it up to about 5500 feet, you were clearly above it.

Looking south toward Ensign Peak, downtown Salt Lake City, and
the Wasatch Mountains at 2:30 PM Sun 11 Dec 2011
Conditions this morning, at least in the Avenues and on the east bench, are markedly better.  This is the result of what I call a "top-down" mixout event.  Temperatures have cooled a couple of degrees at crest level and southerly winds have increased above the valley floor.  This has helped to weaken the inversion at bench level and mix out pollutants.  Compare yesterday afternoon's (purple) and this morning's (red and green) upper-air soundings from KSLC and note how it has dried and warmed between 850 and 775 mb, and cooled somewhat above that.  The changes are subtle, but sufficient for those on the east bench to breathe easy, at least for now.

Unfortunately, a thin lens of cold air remains over the Great Salt Lake and lower portions of the Salt Lake Valley, as indicated by the intense, nearly 10C inversion below 850 mb in this morning's upper air sounding above.  The thin lens can also be seen in the MesoWest surface plot from 1618 UTC (0918 MST) this morning when it was 25–26F at KSLC, but a balmy 33–38F along the east bench near the University of Utah.

Considerable pollution remains in this thin lens, as indicated by the MSI weathercam, which is situated near Olympus Cove and views northwestward toward the Great Salt Lake.

It's possible that the lake breeze will bring the gunk back to the east bench this afternoon, so enjoy the clear air while it is here.

1 comment:

  1. Looks like almost the entire valley south of about I-80 was warmer (and much less smoggy) this morning. I'm giving credit to the weak southerly flow for dragging all this stuff a little to the north, at least temporarily. Would sure be nice to see it mix out entirely.