Saturday, September 20, 2014

Quick Look At Today (Saturday The 20th)

There were some thunderstorms around late in the day yesterday (plot above is of CG flashes through 1 am this morning) - mostly along the Borderlands and also on the Rincons. The towers that broke through into the dry and sheared upper-troposphere were bent over toward the northeast and that will be the case again today. Across the ALERT network during past 24-hours 29 of 92 sites measured rainfall (bit over 30%). Amounts were generally light but there were localized downpours - see post below. Only 3 ALERT sites had over half an inch, with Keystone Peak west of Green Valley reporting 1.22 inches.

This morning there are early showers again. Today the shower area is down to the south (composite radar below is for 7:30 am MST), and Nogales is reporting more heavy rain right now.

This morning's sounding from TWC is shown above. Lower troposphere remains quite moist and CAPE is substantial again. Warm middle-level air continues, although there has been a bit of cooling come around the 500 mb anticyclone center that is over southern Utah this morning. This will be pushed eastward today by the closed low moving ashore over California. Warm air may return from Sonora, reducing CAPE by afternoon. Steering flow will be southeasterly, but shear above 500 mb will remain hostile - quite a strong upper-jet crosses western Arizona this morning.

Dry air with the California low will battle the moist air over southern Arizona this weekend, with the main battle zone stretching south-to-north across central Pima County. By 11 pm on Sunday night the early WRF-GFS forecasts drier air (forecast below for PW at that time) moving into eastern Pima County. Both versions of the model continue to forecast isolated to scattered showers and some thunderstorms today and tomorrow across eastern Pima County.

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