Tuesday, July 29, 2014

Let's Build an Ark!

The University of Utah @ 12:40 PM
The University of Utah is currently experiencing a nice soaking rain, but stronger downpours are occurring elsewhere and could affect us later in the day.

Rdar imagery shows a nice cyclonic (counterclockwise rotating) circulation center over the West Desert.  Although there is widespread shower activity across much of northern Utah, some very strong cells can be found in the Salt Lake Valley and the area around Eureka, not to mention coming off the high terrain in far northwest Utah.

The Oak Springs weather station northwest of Eagle Mountain in Utah County recorded 1.94 inches in the past three hours.  Quite a deluge.  Guess we can turn off the sprinklers for a few days.


  1. (Sorry if this double posts...)
    Jim, care to speculate on how the cyclonic circulation is initiated under the ridge? My two quick thoughts are that the high terrain in Nevada (e.g. the convergence zone) acts almost frontogentically, and that any convergence in that region (which is beneath the divergence aloft) concentrates diabatically generated vorticity. Pretty impressive though how quickly this "developed". Fascinating day in the West!

    1. Neil:

      Large-scale ridge, but clear evidence of a cyclonic PV anomaly on the DT and associated upper tropospheric short-wave trough (http://weather.utah.edu/20140729/images/models/gfs004/GFSSY_WE2014072912F000.gif). This feature moved northward out of the subtropics and perhaps might have originated as an easterly wave, although I haven't bothered to look. I suspect this with the diabtaic heating and low static stability did the job. No need to blame the mountains....


    2. Ah, how 'bout that. My synoptic eyes must be atrophying here in CA. Sure is a cyclonic PV anom ... though the circulation at 700 hPa definitely strengthened over Nevada/UT...

  2. I think these circulation features are centered in the lower to mid levels (evidenced by the tight circulation core with small radius) rather than being primarily upper-level features. So they have tropical rather than mid-latitude characteristics.