Friday, September 02, 2016

Dry-Out For Holiday Weekend

Short of time this morning, so a very quick overview. The plot of detected CG flashes above is for 24-hours ending at midnight last night (from Atmo and Vaisala). Some storms in eastern Pima County, but most activity in broad band from southeast to northwest Arizona (as per at least some of the WRF forecasts yesterday). Again there was more activity in our immediate area than forecast by 06 UTC WRF runs. Rainfall was mostly on or near the Catalinas, Rincons, and Santa Ritas, with some heavy amounts north side of Catalinas (as per 24-hour ALERT observations through 7:00 am MST this morning) below.

Blended PW for 12 UTC from CIRA (above) shows low-level moisture hanging on across southern Arizona this morning. I note that at 12 UTC the GPS PW observation for campus was 1.25", while the sounding data from there indicated 1.40" - quite a difference and I don't know if this has been impacting the WRF runs.

There is probably enough moisture and CAPE for isolated higher elevation storms again over southeast Arizona today. But, as large-scale 500 mb trough takes over the West, conditions become more hostile for storm activity. Below is 06 UTC WRF-NAM forecast of 500 winds and temperatures valid at 5:00 pm MST this afternoon, indicating very warm middle-levels over southwestern Arizona.

The longer-term forecasts indicate seriously dry air over the Southwest for the Holiday weekend. The 06 UTC WRF-NAM forecast of PW (bottom, on 5.4 km grid) is valid at 11:00 am on Labor Day. Looks like we'll have to hope for tropical activity to bring next precipitation event to our region.

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