Wasatch Weather Weenies

Source: http://www.bbb.org 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 st...

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 N...

Strong northerly flow is ushering in much warmer air aloft as a high amplitude ridge builds over the western United States. This is not good news for northern Utah. As Jim “Head Blogger” Steenburgh suggested a few days ago , this massive warm up aloft, which is already apparent in the morning sounding, will isolate a very cold pre-existing air-mass in the valleys of the intermountain west setting up for a persistent cold-air pool… or as Jim put it, “the mother of all inversions.” KSLC 12 UTC sounding. Note the strong northerly flow aloft above the inversion. The warming aloft, which often accompanies the initiation of a persistent cold-air pool, is the result of both subsidence and warm air advection. These two processes occur in concert today along an upper level front , which marks the departing edge of the cold trough that impacted Utah over the weekend. The slowly descending frontal zone will result in a continued increase of 700 hPa (or near ridge top) temperatures ...

Unofficial minimum temperatures at stations reporting to MesoWest suggest that every county in Utah had at least one site with a minimum temperature of -10ºF or lower last night.  The big winner, as usual, is Peter Sink at -46ºF. Beaver                  Merchant Valley                 -20ºF Box Elder             Brigham City                      -20ºF Cache                    Peter Sink                          -46ºF Carbon                  Scofield Dam                     -28ºF Daggett                 Hickerson Park             ...

I'm either a pessimist or a realistic optimist about the forecast for this coming week depending on your perspective.  It looks like a very strong inversion will set in and that it could persist for some time.  From a meteorological perspective, it has the potential to be even stronger than the last.  From an air quality perspective, much will depend on emissions, chemistry, and other factors. This is a long post, but it is important because inversions have such a huge impact on the lives and health of northern Utahn's.  It has two parts.  The first discusses inversion nomenclature.  The second the forecast for the approaching event. a. Inversion nomenclature As discussed recently in a Salt Lake Trib article by Judy Fays , there is quite a bit confusion about the terms used to describe inversions. A cold pool is a topographically confined layer of air that is colder than the air above it.  An inversion is a layer of air in which the temperatu...

I have a simple rule that helps me remember when we are getting to the extremes of temperature in northern Utah.  I call it the 20/20 rule.  Usually, generally, and most of the time the 700-mb (crest-level) temperature lies between +20ºC and -20ºC.  On a very hot day in the summer, the 700-mb temperature is usually about +20ºC.  On a very cold day during the winter, the 700-mb temperature is usually about -20ºC.  If you go beyond those extremes, you are getting into rarified air. Well, we're going to break the 20/20 rule today and tomorrow.  This morning's sounding shows we're sitting at a 700-mb temperature of -20ºC. That is, as the English say, bloody cold, but it's going to get colder.  How about -22ºC by tomorrow morning. And the models keep us at or below -20ºC into Monday.  At the resorts, this is pretty much as cold as it gets.  Expect sub zero temperatures through Monday in the upper elevations. As the storm is tapering ...

The U closed today at 1 PM and we took full advantage by taking a tour in the Avenues Foothills.  There's an impressive snowpack at the top of Terrace Hills Drive (~5000 ft). Good cover on the mountain bike trails. We made a brief visit to the white room.  Yes folks, this was in the Avenues foothills. The snowpack on the north aspect is quite scary.  Facets down low (very soft) and column failures with isolation at the old snow/new snow interface.  We kept slope angles low, which made it a bit challenging to keep momentum going given the depth of the new snow.  Better safe than sorry.     In all honesty, the snow is too deep and too dry for good skiing.  I think the skiing will be better once things settle out some.  When's the last time you said that about skiing from town?