Both the WRF-GFS morning forecast run and also the NAM indicate that low-level winds will become easterly late tonight. This situation complicates the forecasting of minimum temperatures here in the Tucson area because some locales tend to stay windy through the night while others go calm. With below zero dewpoints, radiational cooling will be fierce, and I expect large ranges in the low temperatures within the metro area. The top graphic is the U of AZ WRF-GFS forecast of surface temps and winds valid at 6 am tomorrow morning (30 November 2010) and the lower figure is the same for 6 am on Wednesday morning (1 December). Both forecasts show complicated small scale structure in the wind and temperature fields, especially on Wednesday morning when stronger winds prevail though the night at some spots. Note that temperatures are much warmer on Wednesday morning with some points not getting out of the 40s or low 50s! The WRF forecast for TUS is 29F for 6 am tomorrow morning but 45F for Wednesday morning (current NWS grid forecast lows for TUS are 23F and 29F). Mt. Lemmon is forecast to be 17F at 6 am tomorrow morning but only 33F on Wednesday morning (current NWS grid forecast lows up there are 10F and 23F). Will definitely be interesting to watch how the next two mornings play out.
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