Thursday, August 14, 2014

PW Still High This Morning

This morning (Thursday, August 14th) precipitable water (PW) remains fairly high across most of Arizona, with much of southern Arizona still having values greater than an inch and a half (CIRA blended PW analysis above is from 6 am MST). The GPS PW time series from the campus (below) shows that these high values have persisted for several days now. The early runs of the WRF model at Atmo seem to be too dry this morning. The main thing I noted was that the WRF model forecasts indicate only slight drying during the next couple of days. Both versions of the model forecast scattered storms today from central Pima County eastward.

The morning skewT plot of the Tucson sounding (above from SPC) continues to indicate substantial CAPE present over southeast Arizona. So storms should again bubble up this afternoon, especially over the mountains. The winds remain very light within the lower half of the troposphere and there is almost no steering flow - thus, heavy rain accumulations at localized spots remain likely. Anvil level winds remain fairly strong and are from the southwest. Once again, this is a poor wind profile for many locations in the Tucson metro area. However, I am a bit more hopeful today since there are hints in the forecasts that mid-level winds may turn a bit toward the north during the afternoon, and this could allow a storm or two to build southward from the Catalinas into north parts of the city.

The new forecasts from the NWS NAM model this morning forecast a wet afternoon and evening for southeast Arizona (below is NAM forecast of total rainfall through 5 am tomorrow morning). The crude terrain resolution of this model spreads the rains from mountains into low elevations more than is likely to occur, but the model is certainly forecasting some heavy amounts for high elevations.

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