Sunday, December 20, 2015

GFS Ensemble Plumes Show Large Spreads For Tucson

The current pattern over the north Pacific doe not have high predictability beyond a few days and this is well-reflected by the GFS ensemble plumes for TUS. Above shows QPF forecast by the 21 members with forecasts for the weekend ranging from zero to a bit more than a quarter of an inch. The operational version of the model (blue line) is among the driest of the forecasts. The large spread in the model is emphasized by the forecasts of 850 mb T - below. By Saturday the range of temperatures forecast over TUS span more than 15 C.

For contrast, the QPF plumes for Flagstaff are shown at bottom - the plumes indicate higher chances for precipitation; however the amounts forecast up there still have a large range (from about a tenth to near one inch of water equivalent. Such a spread could mean a skiff of snow or accumulations over a foot! Big difference for local and interstate traffic and also for potential Holiday work loads for the Dept. of Transportation folks.

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