Thursday, September 22, 2011

Some Dry Microbursts Around Yesterday

Yesterday turned out to be quite interesting. Middle-level moisture and a bit of CAPE drifted in along the 500 mb short-wave trough/shear zone that's been west of Baja for several days. This led to some thunder, mammatus, and virga sprinkles. The hot, deep boundary layer below cloud base produced some dry microbursts. Ft. Huachuca had thunder, gusts to 37 mph and a trace of rain. Mt. Lemmon had 0.08" of rain. About 3:30 pm MST I was driving east on Ft. Lowell and passed St. Demetrios Greek Orthodox Church just as a microburst, with gusts to about 40 mph and clouds of dust, struck. It caused some chaos as they were setting up for their 36th Annual Greek Festival, which starts this evening - btw, highly recommended if one can tolerate massive crowds.

Above is last evening's Tucson sounding, which hints at a bit of CAPE around 500 mb. However, the last two 0000 UTC soundings have been way too dry, so it's a bit hard to assess exactly how much CAPE there was (certainly more than the sounding indicated since there were some thunderstorms around). A time-series of GPS PW versus the Tucson sounding PW is shown below - note that last two days the afternoon sounding measured almost 0.25" less than did GPS.

This morning's Tucson sounding has a bit more PW and hints at a bit more CAPE today. Both the Atmo early run of WRF-GFS and the morning NAM forecast isolated showers in southeast Arizona again today.
Image below is looking south from Kitt Peak a bit after 7 am this morning, showing early morning buildups and light showers drifting around.

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