The morning sounding at Tucson was quite moist and unstable, and the key question is how will the thermodynamics evolve during the day? The PW is up above 1.5", after decreasing some yesterday afternoon. Winds aloft below 300 mb are now from the south-southeast at 20 to 30 kts, indicating quite a change from over the weekend. Temperatures at 500 mb are a cool -8C over most of Arizona. The surface easterly winds continued strong yesterday until around 4 to 5 pm MST. However, they too have switched to the south this morning, as the circulation over southern Arizona now reflects the closed low over northern Baja. Today the early WRF-GFS forecasts several rounds of thunderstorms over eastern Pima County during the afternoon and evening. Total predicted rainfall through midnight tonight is shown above. The model still forecasts heaviest activity to the west-northwest of Tucson, but it predicts a substantial increase over eastern Pima County. The model does appear to clear away the clouds too quickly in its forecast - solar irradiance (W/m2 at noon) is forecast to be quite strong by the end of the morning. So, the clouds could be the main problem for today. However, I think that the model trend looks good, after many suppressed afternoons locally.
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