Thursday, July 23, 2015

Morning Showers Equals Difficult Afternoon Forecast

The morning showers obscure the Catalinas at 6:36 am MST (above). Appears to have been a bit more measurable rain here at house, but airport has reported moderate rain, 76 F, and south-southeast winds at 15 mph. The showers do not reach much above 25,000 ft MSL and there have been no lightning flashes detected. The visible satellite image below (from 1340 UTC) shows a thick cloud mass covering much of northern Mexico and eastern Arizona, which will cause difficulties this afternoon, as temperatures will likely not make much of a rebound.

The TWC morning sounding plot (below from SPC) is very moist, and there will be substantial CAPE present later today at spots where there is some sunshine, especially at higher elevations. The issue, of course, will be whether morning outflows completely dominate and shut down afternoon activity. Winds remain quite light, except in upper-half of troposphere - another day with marginal steering winds but potential for heavy local rains and perhaps wet downbursts. 

The WRF-NAM forecast from 00 UTC last evening appears to have forecast the early morning showers most accurately of the various models. It forecasts limited thunderstorm activity during the afternoon, as opposed to the 06 UTC runs which forecast a very active afternoon across eastern Pima County. Setting is one in which we'll just have to watch the situation evolve and also take a look at the new 12 UTC WRF forecasts from Atmo.

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