Thursday, November 29, 2012

Cold Pools, Cold Puddles, and Lake Breezes

During inversions, meteorologists frequently call the airmass beneath an inversion a cold pool.  The name seems appropriate as the dense air, when it is full of pollution or topped by clouds, behaves in much the same way as a pool of water.

In some instances, however, the cold pool is incredibly shallow.  As such, it might be better labeled a cold puddle.  One could observe lingering pollution in such a cold puddle yesterday afternoon over the Great Salt Lake and and lower elevations of the northern Salt Lake Valley.

Pollution in an extremely shallow cold pool (a.k.a. cold puddle) over the
Great Salt Lake and lower elevations of the northern Salt Lake Valley at
about 5 PM MST 28 Nov 2012 (click to enlarge)
That cold puddle represents the last remnants of our latest inversion event, which was extremely persistent over the Great Salt Lake.  One can see the cold puddle pretty well in the surface analysis from 5 PM MST yesterday.  Check out the incredible 12ºF temperature contrast between the two sites that are less than a mile apart at the Salt Lake Airport.  This contrast represents the boundary between the cold puddle and warmer air.

Source: MesoWest
For most of the day, the Salt Lake City airport was in the warm air, but the temperature dropped abruptly about 14ºF as the cold puddle pushed in.

What is happening here is that an extremely shallow puddle of cold air remained entrenched over the Great Salt Lake.  That cold air eventually pushed southward and eastward into the Salt Lake Valley with the Great Salt Lake breeze yesterday afternoon.  The temperature contrast accompanying the Great Salt Lake breeze was greatly concentrated thanks to the warm southerly flow ahead of it.

The Salt Lake City Airport and areas to the west can sometimes feel like another planet compared to the University of Utah and the east bench, and that was the case late yesterday afternoon.


  1. I think this case highlights some very interesting patterns. Based on surface temperatures, the Salt Lake and Tooele valleys usually appear to have some of the deepest mixing of anywhere in the state once the surface cold pool is pushed out. SLC has been even warmer than St. George much of the last 24 hours, essentially dry adiabatic to 700 mb which most of the state has not been, at least until now. Most of the I-15 corridor in general (Ogden to Cedar City), also seems to mix out fairly readily in southerly wind patterns. Further west in the Salt Lake Basin, mixing was much poorer. The area around Wendover barely warmed above 40 degrees yesterday, and was 32 last night while SLC was 56. The station at Lakeside Mountain, west of the lake at just over 5,000 feet has remained in the 40s, implying that the cold puddle is somewhat deeper on that side of the basin. Fascinating stuff!

  2. I didn't mean to imply that 56 was the low temp at SLC... that was from the ob last evening around 10 pm.