This morning (Thursday, 22 December) a 500 mb closed low is over central Utah and moving toward southern Arizona. The 500 mb temperatures in its core are -30 to -35C, and Atmo's early WRF-GFS forecasts the 500 mb temperature to fall to nearly -30C over Tucson by morning tomorrow. The system will bring a deep, cold air mass across southern Arizona today, but with little precipitation, except in the White Mountains. The main brunt of the winter storm will be in Colorado and New Mexico. Graphic below shows the early WRF-GFS forecast for total precipitation through midnight tomorrow night.
The WRF-GFS forecast of snow accumulation for the same period is shown above and indicates a bit of snow on the Catalinas, with better amounts over the Chiricahuas and Mt. Graham. The tabular forecast from the WRF-GFS (below) indicates coldest temperatures over the Tucson Metro area around sunrise tomorrow morning. The model keeps the temperatures warmer, and mostly above freezing in the city on Saturday morning. Once again a situation where low temperatures will be a difficult forecast and depend to some degree on the winds during the night. It seems that the Christmas light spectacle in Winterhaven (a neighborhood just south of our house) is a magnet for bringing in cold and rain to dampen the hay rides through the neighborhood.
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