First - the synoptic situation has changed rapidly with a bulding high at 500 mb over the Great Basin pushing the portion of the Pacific trough that was over Arizona to the southwest. Winds at 500 mb this morning are from the south and there appears to be a weak cutoff low at 500 mb over northern Baja. To the east over the Southern Plains and new Mexico, there is another weak backdoor front acting to push low-level moisture (for example, El Paso has a much more moist sounding this morning than does Tucson) toward southeastern Arizona. The Tucson sounding is shown in the top image - it shows a very deep elevated mixed layer (in temperature) which is yesterday's residual boundary layer. The Tucson Td data are too dry (see middle graphic comparing TWC PW with GPS PW) by about 5 mm or so, likely due to a bad Td profile in the old boundary layer. Thus, we are now in the time of year when the bad PW data from the RRS sondes will impact forecasts of convection.-------------------------------------------------
Second - It appears that deeper and stronger convection will remain mostly to the east today but that a nice influx of low-level moisture may come in by tomorrow morning with the help of outflows and the backdoor front. The bottom image shows that moderate cumulus have already developed over the Catalinas. The cloud structure appears to fit nicely with the sounding data above 600 mb - looks like bases are around 550 mb and the anvil (if one coould call it that) is only at 450 mb or so. Regardless, it's a good thermodynamic environment to support dry microbursts, if moderate convection, with snow or graupel virga, move out over lower elevations.
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