Thursday, February 17, 2011

Models Not Forecasting Much For Southeast Arizona At This Time

 Heavy clouds hanging on the Catalinas this morning Thursday 17 February 2011). Cloud cover during the night kept the morning low at a very mild 54F - the warmest morning low here at the house since last October or early November!

Situation at 500 mb is very complex over the Pacific and western North America - GFS analysis at 1200 UTC is shown above. The sytem out near Hawaii has produced another long plume of high PW that curves eastward to northern Baja. What is not clear at this time is whether the short-wave trough/cutoff forecast to affect the Southwest this weekend will be able to pull this richer moisture northward. There is a massive 500 mb ridge extending northward across the Bering Sea and one stream of vorticity is digging south along the eastern side of the ridge, while several other vorticity maxima are along the west coast, having had their origins in the large, cold cyclone over Canada. It's not clear how well the models will do forecasting the details of the evolution of the current plethora of vorticity maxima - we'll have to watch as all this sorts itself out over the next couple of days.

The two precitation forecasts above are from the midnight run of the Atmo WRF-GFS and and this morning's 12 UTC run of the NWS NAM model. The WRF (top) forecasts no precipitation in the metro Tucson area through 11 am Sunday morning, keeping the event confined higher elevations. The NAM (bottom) forecasts no precipitation over southeast Arizona through 5 pm Sunday afternoon, keeping the significant precipitation amounts over the Rim country and northwest mountains.

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