The 500 mb NAM initial analysis this morning (above) indicates that a poorly organized ridge, with numerous embedded weak features of both cyclonic and anticyclonic natures, continues to prevail across most of the Southwest and Mexico. Winds are very light through the lower troposphere below 400 mb. Above 400 mb Pacific westerlies (i.e., a Fall flow pattern) are present to quite low-latitudes, with dry air aloft over most of Arizona. It's not a pretty picture.
The Tucson and Phoenix soundings continue to have a nice amount of residual moisture present with PWs of around 1.50" in the southwest part of state and around 1.25" in the south central (note that the Tucson RRS sounding appears to be about 0.20" too wet this morning). Low levels have cooled around 5-6F after yesterday's storms and, although the soundings have CAPE, it's not clear whether there will be enough heating to re-establish a single, deep boundary layer. It appears most likely that there'll be an afternoon air mass over low elevations that'll need a nice kick from mountain outflows. There is substantial CAPE at high elevations and the mountains will be able to bubble away very nicely, given the low shear up to 400 mb. It appears that what steering flow there'll be will be northerly. My guess is that there's a 50 to 60% chance of a storm here at the house, since conditions appear favorable for Catalina Mountain thunderstorms to come down our way.
The models forecast the next two days will be stormy and wet, as a weak trough moves across the state from west to east. I'll watch day-by-day and also hope that everyone has a great Labor Day weekend.
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