There were numerous thunderstorms across southeast Arizona yesterday, producing frequent lightning and strong winds - there were a number of reports of severe winds in the Tucson area. However, rain amounts were generally light because of the very high cloud bases and somewhat limited CAPE. Here at the house we had several different thunderstorms, with an evening storm producing wind gusts of 40 to 50 mph, but only 0.04" of rain. Areal coverage of rainfall across the ALERT network was a bit over 60% for last 24-hours, but only 5 stations had half an inch or more. Max reported was 1.26" on the northwest side of the Catalinas. Photo above was taken at sunset, looking west through light rain.
Storms from southeastern Arizona grew into a large MCS that moved into the northern GoC, with a second large MCS developing just to its south. The IR image above from 1330 UTC this morning shows the decaying, convective system over the GoC. Hurricane Gilma is far southwest of the southern tip of Baja.
Image below is 1345 UTC water vapor, showing very dry upper-tropospheric air circulating around the anticyclone and heading west toward Arizona. We usually think of dry air coming into Arizona from the southwest to northwest. But, as Mike Leuthold said in his discussion yesterday, this situation is like a typical Plains dryline, except it's going the wrong way.
The early run of Atmo's WRF-GFS model forecasts the easterly dry-out to be halfway across Pima County by 4 pm MST (above is PW forecast valid at 4 pm). Timing is everything today, as the model forecasts storms to develop ahead of the "dryline", but just out to the west of the Tucson area (see model forecast of 4 pm composite radar echoes below). Once again, what's 100% certain is that it will be hot - yesterday's high of 108F at the airport was a new record for August 8th.
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