A number of interesting changes are underway, even though we are still under the influence of the 500 mb trough to our northeast. Surface temps and dewpoints are up a few degrees compared to 24-hours ago, and SLP is down 2 to 3 mb in the same period. Thus, a nice slosh of low-level moisture occurred during the night. The deeper, subtropical moisture is poised to push back north across the border - see previous post - and things should be much improved during the night and tomorrow wrt low-level moisture and CAPE. The morning Tucson sounding (top image) might have a bit of CAPE left at dusk, but certainly not much - even though cooler middle level temps have moved in from the west. The vertical wind profile this morning is not good - winds below 500 mb are west to northwesterly (which means a strong diurnal circulation from off the lower deserts this afternoon that may bring drier air with it). Winds above 500 mb are west to sothwesterly and much stronger than the low-level flow.------------------------------------------------
The RAP 500 mb analysis for 12z this morning (middle image) shows that the lobe of the subtropical anticyclone currently affecting the Southwest is centered off over northern Baja - not a good positioning at all (and unfortunately the 700 mb anticyclone is also out there this morning). However, up at 250 mb there is just a single, well-defined anticyclone that is centered over the Big Bend country of Texas. So, the overall setting is a bit chaotic this morning; however, this morning's NAM forecasts indicate a gradual improvement during the day and night. The 500 mb anticyclone is forecast to shift northeastward across south-central Arizona and be over western New Mexico by this time tomorrow. The 250 mb anticyclone shifts westward into northern Mexico - the net result being a much improved vertical wind profile by tomorrow.
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It appears that most activity today will be along the Borderlands and in Mexico and that cores will tend to move toward the south. However, with a good push of low-level moisture into southern Arizona during the night, activity should be much increased tomorrow. Indeed the NAM forecast of precipitation for the 12-hours ending at midnight tomorrow night (bottom image) has centered the action almost directly over Tucson. So, it will be very interesting to see what the morning U of A WRF runs indicate!
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