Friday, October 16, 2015

Will Today Be Better For Rain On Ground?

Yesterday the thunderstorm activity was again most intense out in California, however, there were some storms along the Arizona borderlands from Nogales eastward. Plot above of CG flashes (from Vaisala and Atmo) is for 24-hours ending at 12 UTC this morning. While there were dreary skies much of the day here, the high-based, sprinkle showers did not produce much rain on the ground. Across the ALERT network only 4 high elevation sites measured 0.04" during past 24-hours. I scanned the RAWS and ASOS observations across southeast Arizona and only found one station with a tenth of an inch or more - that was Douglas with 0.13". So pretty much a dud day in the way of rain.

The showers yesterday were ahead of a weak short-wave moving northward out of the northwest Mexico/east Pacific data voids. This S/W shows up nicely in the 14 UTC IR satellite image below and currently arcs from near Las Vegas across northern Arizona and into Mexico south of the New Mexico boot heel. Of interest to us is the trailing short-wave over and west of northern Baja. This feature will move across our area this afternoon and tonight, perhaps accompanied by stronger convection and some rainfall (current POPs for airport from NWS are 60% for today and again tonight).

The situation is however complicated, as usual. A back-door front is moving into southeastern Arizona from New Mexico this morning (there is a strong pressure gradient at the surface from here to northeastern New Mexico of around 15 mb). The 06 UTC runs of the WRF models at Atmo bring the east winds across our area - above is forecast of 10-m winds from WRF-GFS valid at 11:00 am MST this morning. Such situations are often accompanied by drying, with storms developing to our west or northwest.

However, the model forecasts concurrent moistening (note that the morning TWC sounding has little CAPE and PW of 28 mm). The forecast skewT for TWC below is from the WRF-NAM version and is valid at 3:00 pm this afternoon. The PW has increased to 32 mm and CAPE is over 1000 J/Kg - so very interesting changes in the model forecasts. Both versions are forecasting thunderstorm activity for our area this afternoon and evening, with considerably more rainfall occurring also. Should be an interesting day for weather watchers.

No comments:

Post a Comment