Yesterday proved to be quite suppressed relative to day before, so a bit of a zig-zag in some of the models. Radar chart above is from 9:00 pm MST last evening. Main impact was that there were no significant outflow boundaries sloshing around during the night and dewpoints here in Tucson remained low. The morning sounding from TWC (below) shows the old, hot and dry BL in place this morning, with the nearly adiabatic temperature layer extending up to above 500 mb. A very potent thermal structure.
The large-scale circulation and pressure pattern is pushing low-level moisture westward from southern New Mexico and the Big Bend Country - my quick surface analysis for 7:00 am above indicates dewpoints of 50 to 55 F are literally just to the east of metro Tucson.
The forecast sounding for TWC (from the WRF-NAM 06 UTC forecast run) below is valid at noon today. The model forecasts PW to increase from the morning observed value of 21 mm to values around 35 mm - a significant increase that results in considerable CAPE. Although forecast steering level winds are light, the deep BL combined with the CAPE indicates the likelihood of severe thunderstorm winds for eastern Pima County this afternoon.
Both the NAM and GFS versions of the WRF model 06 UTC runs forecast explosive development of thunderstorms during the early afternoon today. Timing may be a bit of an issue, since the models brought the low-level moisture in several hours too soon. But, regardless, the potential exists for severe storms this afternoon and calls for careful monitoring of the situation.
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