High Clouds from Pacific Over Tucson Area And Much Of Southwest

We've been away a couple of days but are now back after the Holiday and looking forward to a new month.

December starts here with a fairly wide-spread cloud cover, high clouds and some middle clouds, intruding into the Southwest. Visible image above is from 8 am MST this morning (December 1st).

The MIMIC PW analysis from CIMSS (Univ. of Wisconsin - below) is for 12 UTC this morning. The large closed low apparent to the west of California is forecast by current model runs to weaken rapidly as it moves eastward. This circulation has a narrow atmospheric river wrapping into it. However, a much more substantial and broad moisture plume from low-latitudes is pushing northeastward toward southern California and models indicate that this plume will also wrap into the weakening middle and upper level system. This moisture will spread over Arizona tomorrow, bringing an unsettled day with some winds, virga, mammatus, and some light showers.

The early run of the WRF-NAM at Atmo forecasts a fairly rapid moistening of the atmosphere as the moisture plume moves overhead tomorrow - above is the model's forecast of the sounding for TUS at 5 pm tomorrow. PW has increased from only 7 mm at initialization time to almost 30 mm. The model does not develop much in the way of CAPE, but the deeply saturated environment (assuming the forecast verifies well) should support some showers. The model's forecast of accumulated precipitation (below) through 11 pm Wednesday night keeps meaningful precipitation to our north. However, the forecast appears a bit conservative to me, given the forecast sounding, so tomorrow may be more unsettled than indicated by the forecast model.