Thunderstorms moved across parts of the metro area yesterday afternoon - view above is from 5:00 pm MST and composite radar below is from 5:05 pm. The storms tended to split around the core metro area - here we had a rumble of thunder, a spit of rain and a bit of outflow cooling - end result a Trace. The airport however had 0.10".
Plot above from the ALERT network is 6-hour rainfall ending at 5:15 pm. As storms moved westward, most stations in west thrid of network picked up rainfall with amounts generally less than half an inch. The CG flash density plot (below for 24-hours ending at 6:45 am this morning - from weather.graphis and Vaisala) shows that yesterday was an active thunderstorm day for northern and southeastern Arizona.
Today we have the inverted trough from the east moving across northern Mexico and southern Arizona. The 12 UTC 250 mb analysis above (from SPC) shows the large scale of this IT and the strong upper winds associated with it. The water vapor image below is from 7:30 am and shows that mid to upper tropospheric dry air is wrapping around the IT from the east. The degree of drying that will occur today presents a forecast quandary.
The TWC morning skew-T plot (below - also from SPC) indicates PW at 46 mm, a much strengthened wind profile, and substantial CAPE. All in all, an excellent situation for severe thunderstorms here. However, the WRF model forecasts from Atmo indicate considerable drying by afternoon with the PW dropping a huge amount, reaching 28 mm at 3:00 pm. This drying and warming above 500 mb leaves only a sliver of CAPE by that time and storms develop to the west and south of Tucson. The 00 UTC runs are not quite so dry, but still tend to keep storms to our west and south. If the models are too dry and stable, there will be an excellent chance for storms to move from mountains across metro again this afternoon - but if forecasts are accurate we'll mostly be looking to the west at Cbs.
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