Wednesday, August 09, 2017

Another Day Under The Anticyclone

We have been away attending to family matters in the Midwest since early Friday morning, and on our return I found an absolutely dry rain gauge. So we were away during a dismal break in thunderstorm activity and return to find a setting that may begin to improve a bit over next several days.


Pleasant and dry this morning (especially compared to last several days of high humidity in Midwest) at sunrise with a few middle clouds drifting around (above).

Plot below shows CG flash density over western U.S. for the 24-hours ending at 6:30 am MST this morning (from weather.graphics and Vaisala). Thunderstorms were confined to mountainous areas well north and east Arizona.



The morning skewT plot of TWC data (above - for 12 UTC from SPC) shows an unorganized pattern in both winds and thermal structures.  There are two layers of light and variable winds (surface to 700 mb and aloft from below 500 to about 400 mb) with southwest winds between and above. If thunderstorms develop the dominate steering might be from the southwest or indeterminant. Yesterday's old BL extends to almost 500 mb and troposphere is split into two halves by the nasty temperature inversion just below 500 mb. The moisture was well-mixed only to 700 mb. All-in-all quite a mess. The 500 mb anticyclone is a bit off to east or northeast and exhibits very warm temperatures in middle levels.

The 6 UTC WRF-GFS forecast sounding for TWC is shown below for same time as the observed above. Although PW is quite near the observed value of a bit over an inch, there are considerable differences in the thermal and wind structures below 600 mb - especially with the stronger and more organized east flow above surface. This is an important difference, since PW is higher toward El Paso - will stronger east winds develop this morning? The capping inversion near 500 mb is very much under-done in the model forecast, and this will be a formidable cap, especially for low-elevation convection.



The WRF-GFS forecast for TWC valid at 4:00 pm this afternoon (above) indicates light westerly winds in the BL, but with increased moisture in well-mixed layer. There is CAPE in the forecast, but the warm middle-levels may again be under-done. The forecast sounding, valid at same time, for Sonoita (below) indicates much more favorable conditions nearby, but at elevations of about 5,000 ft MSL.

Bottom line to all this is that there may be storms on the mountains from north to east to south of metro area. These would be producing mostly light to moderate rains and gusty winds and would have difficulty moving off the mountains. 

Increasing low-level moisture from GoC in a day or two may improve the convective situation considerably.




2 comments:

  1. Great timing of your Midwest trip!!

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  2. Hi Stefan - if you are still at DM please let me know your email address - Thanks Bob@squidinkbooks.com

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