Saturday, July 18, 2009

Strong Storms Yesterday with Wind Damage

There was more widespread storm activity yesterday than on Thursday and the storms occurred in the late afternoon. There were numerous reports of wind gusts over 40 mph from Luke AFB south to Sells and east to the White Mountains. Safford had lots of wind damage and bad dust in the area and measured a gust to 63 mph. The Black Hills RAWS station measured a severe gust of 57 mph and Horse Camp RAWS and Casa Grande ASOS measured gusts of 54 mph. The ATMO rooftop anemometer had a gust to 75 mph. Yesterday’s storm setup was about as synoptically evident an event as occurs out here in the Southwest.

Today is more complicated. The PW trends have been down everywhere except out at Yuma, and as Mike Leuthold mentioned yesterday, the models forecast more drying this afternoon over southeast Arizona. The NAM gradually shifts the 500 mb anticyclone from western Utah toward the Four Corners by evening and then southward toward the Chirachuas tomorrow afternoon. Thus, the favorable wind shear environment for strong storms will continue through this evening but CAPE will be on the wane.

The TWC morning sounding is quite interesting. First, GPS PW values indicate that the sounding is too moist by about a tenth of an inch. There are two, deep residual boundary layers present – one from about 920 to 670 mb and the second from about 630 to around 450 mb. Thus, the entire lower half of the troposphere has a very strong temperature lapse rate. There were ACC floating around at sunrise, indicating the instability present at the top of second residual layer. So, it appears to me that the situation today favors very high-based storms that move westward from the mountains producing microburst/downbursts at lower elevations where it will be very hot.

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