Wednesday, June 29, 2011

Significant Changes Past 24 Hours

Yesterday afternoon there was quite a bit of thunderstorm activity in southeast Arizona and northern Sonora. For the first time this summer, a Cb was visible from the house. Photo taken about 4 pm is above - note that it is a "fuzzy" and not very impressive storm, but nevertheless the first one this month.

 The composite image for about 4 pm from NWS KEMX radar is shown above. The storm in photo is the echo located near Green Valley. The radar coverage is substantial, and June 28th goes into my weather log as the first day of the 2011 summer thunderstorm season. The NWS TUS observations indicated lightning to distant southeast at 4 pm and to distant northwest at 10 pm (the second lightning observation probably should have been to the southeast also, since there were no storms to the northwest).

There was a large MCS over northern Sonora, as captured in the WV image above from 10 pm last evening. The outflow from this MCS was quite large and moved northward across much of southeastern Arizona, producing strong gusts, some sprinkles, dust, and put a smell of rain into the nighttime air. The outflow passed the airport (TUS) before 11 pm and the wind gusted to 32 mph; Ft. Huachuca had a thunder-sprinkle; and Safford had a sprinkle with a gust to 54 mph. The RAWS station at Guthrie had a gust to 57 mph (probably the first severe convective event of the summer in southeast Arizona). [Mike Hardiman alerted me that it takes 58 mph for a gust to be severe - so much for my memory!] The Rucker RAWS site measured 0.11" of rain. No rain was observed in the Pima County ALERT network.

24-Hour Precipitation in Sonora, Mexico (mm)
Banámichi (25 milímetros)
El Cubil (16)
Nacozari (15.5 milímetros)
Arizpe (13.3)
Paso Nácori (11.5)
Aribabi (9.2)
Tepache (8.5)
The TWC morning sounding shows that the moist, outflow air extends up to about 800 mb. The skies at sunrise were quite dirty and hazy, with both suspended dust and the increased moisture. The temperature here at house when I returned from my walk (6:30 am) was at 84F. So the outflow didn't bring much in the way of cool air, but it did result in another incremental increase in low-level moisture. Note that this is downdraft-recycled air and moisture, not a full-blown intrusion of the subtropical mT airmass. I can modify the sounding and get a small amount of CAPE this afternoon above 500 mb. The WRF forecasts substantial thunderstorms to move northward across the Tucson area between 3 and 6 pm this afternoon. If this happens, the storms should be high-based and could produce winds reaching severe levels (56 mph or higher).

The times series of GPS PW above shows the PW increase over the past two days and indicates that for the first time in a number of days that the TWC sounding and GPS data are in agreement over the amount of PW present! So, it should be an interesting day - more later, including a look at TS Arlene and how she might impact our weather.

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