Thursday, January 17, 2013

Stacked Like Pancakes

The lid is now tightly closed on the Salt Lake Valley and we have inversions and stable layers stacked over us like a good pancake breakfast.  Until last night, the inversion developed mainly due to warming at upper levels.  This was due to the presence of a layer of stratus clouds, which resulted in the low-levels warming somewhat rather than cooling.  Yesterday, however, that stratus layer dissipated and temperatures dropped like a rock overnight along the valley floor.  With some effort, you can see this in the evolution of upper-air soundings taken from the Salt Lake airport over the past several days.  Note in particular the abrupt drop in temperatures near the bottom of the sounding between the last two frames, which are from yesterday afternoon and this morning.  

KSLC Upper Air Soundings from 1200 UTC 13 Jan – 1200 UTC 17 Jan 2013
Zooming in on this morning's sounding, we can see three major inversions or stable layers.  The highest is the large-scale inversion produced by warming aloft.  The base of this inversion sits about 2000 feet above the valley floor and it essentially caps all the clouds, haze, and smog that we have in the valley.  

KSLC Upper Air Sounding at 1200 UTC (0500 MST) 17 Jan 2013
Beneath this inversion is a stable layer.  The University of Utah and most of the east bench sits in this stable layer.  Finally, very near the surface there is a nocturnal inversion that formed last night.  Within this inversion it is much colder, with fog in places.

Life is very different depending on where you are relative to these inversions and stable layers.  At the Atwater Study Plot near the base of Alta, which is above the large-scale inversion, overnight temperatures remained at or above 25ºF.

Source: MesoWest
At the University of Utah, which was beneath the large-scale inversion and within the intermediate stable layer, temperatures fell into the mid teens.

Source: MesoWest
At the airport, which was within the shallow nocturnal inversion, temperatures dropped into the low single digits.

Source: MesoWest
This provides a nice example of the complex layering of the atmosphere that sometimes occurs during our inversion events, especially at night.  The nocturnal inversion will probably weaken some today, but, thanks to the large-scale inversion, the valley is entirely cut off from the clean air above.  And that is the way it will stay through early next week.  The models are hinting that a cold front may move through Utah on Wednesday.  Let's hope that comes to fruition. 

1 comment:

  1. Ya I live in West Bountiful between legacy and I-15 and the temp dropped to -2 and we had dense fog move in, elevation make s a big difference I guess!