Monday, July 23, 2012

The Care and Feeding of Utah Convection

With a strong ridge of high pressure centered over the central United States, the large scale pattern is presently ideal for the care and feeding of Utah convection (i.e., thunderstorms).  Even though the large scale flow over northern Utah is out of the southwest, it originates in the tropical and subtropical easterlies that are characteristic of the North American Monsoon.  

1200 UTC 21 Jul – 1200 UTC 23 Jul IR Satellite Image and
GFS 500-mb streamline analysis
As a a result, dewpoints are elevated and we're seeing some rumblers across the state.  In St. George, where some thunderstorms moved through overnight, several sites are presently reporting a dewpoint of 67ºF.  

But it's a dry heat, right?  Here at the U, things aren't quite so humid, but the dewpoint is still 53ºF.

For comparison, our average for this time of day in July is about 41ºF.  Those of you with swamp coolers will probably find their effectiveness is lower.  

With all this moisture in place, perhaps Thor, God of Thunder, will pay us a visit again tonight.


  1. Yesterday's show was an awesome light show in west bountiful, but not much rain, why was this the case with the dewpoints so high?

  2. I think the cloud bases were still quite high early on, the dewpoint at the surface really didn't come up that high until it rained which might explain the fairly light totals. Also, with very little wind shear present last night, several of the nocturnal convective clusters developed cyclonic rotation including one over Tooele County, one or two in Nevada and a large one in southwestern Utah. The latter of these still has a noticeable rotation as it moves north across Beaver and Millard Counties this morning.