Yesterday was quite suppressed across Pima County, as per the WRF-GFS forecast. No deep convection and no rain, except in the distant mountains and along the borderlands of southeast Arizona. View above is of the Catalinas at 3 pm MST yesterday. This morning there is heavy debris cloud from Sonora drifting around.
The Tucson morning sounding has little CAPE, but PW has recovered to around 1.5". Will things get better or worse during the day? The WRF-GFS, on the 5.4 km grid, forecast valid at 6 am is shown above for 850 mb Td. The dry air intrusion over western Pima County is a definite issue in the forecasts for today. It's scale is small enough that it is invisible to the upper-air network - so the first question is whether or not that dry air is really out there. GPS PW data (Sells and Organ Pipe) say yes and the sunrise dewpoint at Sells was only 47F, compared to low 60s here in the Tucson metro area. So, my answer is yes, that dry air is apparently lurking to our west, as per the model forecast. The WRF-GFS (on the 1.8 km grid) forecasts drying at 850 mb over eastern Pima County this afternoon. The net result of westerly winds below 700 mb in the model's forecast is a minimum amount of CAPE over southeast Arizona this afternoon (below is CAPE forecast valid at 5 pm MST).
The model seems a bit too dry in its forecasts of PW this morning, so that would be the parameter to keep an eye on as the day progresses. The total rainfall forecast through midnight tonight (below) indicates only some sprinkles and spits, with meaningful amounts in the Rim country and south of the border. Should be an interesting day to watch how the model does - also definitely a day to take a close look at the 12 UTC runs from Atmo.
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