Thursday, August 22, 2013

Drying From East This Afternoon?

Cloudiness persisted into early afternoon yesterday and eastern Pima County was very suppressed - above shows CGs during 24-hours ending at 6 am this morning (22 August). Only 4 ALERT stations reported rain - all at 0.04" with 3 up in the Catalinas and the other far south at Tubac.

This morning's sounding at Tucson (above) indicates some CAPE, especially at higher elevations. Cloudiness this morning is mostly off to west and southeastern corner of Arizona is mostly clear. Steering flow is from the east-southeast. However, contrast Tucson with El Paso's morning sounding (below). Note that the air off to the east is much drier and that there is an ugly inversion and warm middle level air at and above about 550 mb. So, the forecast challenge is predicting how far west the El Paso air will be when storms begin developing ahead of it. The current CIRA blended PW product indicates leading edge of dry air is located along the Arziona/New Mexico border.


The early runs of the two versions of the Atmo WRF model have forecasts that are quite different. Shown here are forecasts of composite radar echoes valid at 4 pm MST this afternoon (WRF-GFS above and WRF-NAM below). The GFS version still has some strom activity in eastern Pima County and the NAM version has the major area of activity out in southwest Arizona. So again, observing will be easier than forecasting for the short-term.

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