The 6 am image above shows the Catalinas at sunrise this morning (Monday Sept. 14, 2009) and the mystery is: What are those low clouds doing there down on the mountain tops?
A look at the morning observations shows that there is southerly, moist flow over southeastern Arizona below 700 mb. This weak push of moisture has lead to an interesting situation. The thermodynamics could evolve today to produce a moderate amount of CAPE over much of the eastern third of the state. This would be happening in an environment that's atypical of the Southwest in summer. The morning sounding (which is a bit too wet) indicates a veering wind profile below 700 mb with moderately strong westerlies above - i.e., a wind profile more like the classic storms environment of the Plains, albeit weaker.
The 500 mb trough along the west coast has a strong negative tilt and is digging ashore all the way into northern Sonora. Ahead of this trough the upper-level flow is highly difluent, while the lower-level winds have become southerly. The NAM indicates that the southern end of the trough is going to swing rapidly across southern Arizona as it pulls inland and northeastward. This will bring subsidence and drying behind it.
Thus, there seem to be two possiblities today for southeastern Arizona - a rapid drying as the trough swings in before storms get going, or - storms occur in the east and northeast ahead of the trough. Storms that do occur would have some possiblity to be severe given the setting and a supercell or two would not that surprising.
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