Tuesday, December 20, 2016

Subtropical Moisture Plume Moving North This Morning

The upper-level cyclone west of southern Baja is advecting substantial, low-latitude moisture northward toward the Southwest. The IR satellite image above is from 1230 UTC, while the MIMIC PW analysis below is for 1000 UTC. The higher moisture, which stretches south to very low latitudes, is reaching the northern half of the GoC already.

The forecast of PW above (on 5.4 km grid) is from the 06 UTC run of the WRF-GFS model at Atmo and is valid at 11:00 pm MST tomorrow, December 21st. Values of an inch or more have intruded into southern Arizona in this forecast.

The 06 UTC GEFS QPF plumes for the airport are shown above. The ensemble members are now more consistent with forecasting rainfall at the airport - 100 % of the members forecast rain late tomorrow for period extending to Friday afternoon, and amounts are now considerably higher, with average exceeding 0.60 inches. Timing, however, is much less certain in the ensemble forecasts. A second event on Christmas weekend is even more uncertain in the model forecasts, with large differences in the speed of that system between the GFS and ECMWF.

So, focusing on the first event, the 06 UTC WRF-GFS forecast (on 1.8 km grid) of total precipitation through 11:00 am on the 23rd is shown below. If the forecast verifies, this will be a substantial precipitation event, especially for southeastern Arizona.

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