A Strengthening Inversion with an Uncertain Future

Weather balloons launched from the Salt Lake City Airport show the strengthening and descent of the inversion over the past four mornings.

Loop of 0500 MST soundings from 31 Dec 2012 and 1, 2, and
3 Jan 2013.

During the period, the 700 mb (near mountain-top level) temperatures increased from about -15ºC to -5ºC, whereas the surface temperatures decreased from about -8ºC to -12ºC.  This produces a 9.4ºC temperature inversion this morning between 814 and 720 mb (6280 and 9400 ft).  Yup, we're pretty much screwed.

About the only positive thing in this instance is that the base of the inversion is at 814 mb (6280 ft).  This means that the pollution can mix through about a 2000 ft deep layer this afternoon before it hits the capping inversion.  That will keep pollution levels lower than if the inversion were closer to the valley floor.

I've been quite concerned about this event given the model forecasts for the development of a very stagnant pattern over the western US, but the latest GFS forecast has changed dramatically from yesterday.  Rather than closing the approaching trof off the California coast and ultimately setting up a Rex block (see previous post) it is bringing into the western US as an open wave.  This change can be seen by comparing the forecast from yesterday's 0600 UTC GFS forecast (top image below) to today's 0600 UTC GFS (bottom image below) for 1800 UTC (1100 MST) Sunday.

Let's hope something close to the more recent run verifies, as it would break up the inversion on Sunday and give us some snow for the mountains.  I'll be more than happy to wipe egg of my face for a crappy long-range forecast if that happens.