The weather here in the Tucson area and southeast Arizona will continue unsettled as we head toward Christmas. This is well indicated by the current NWS forecast probabilities of precipitation (POPs) at the airport - Wed 50% Wed Night 70% Thur 70% and Sun 30%.
However, the global forecast models (GFS vs ECMWF) have considerably different details within their respective forecasts. Shown above are the 500 mb forecasts valid at 5 pm MST on Wednesday (GFS top and ECMWF bottom). The short wave and vorticity maximum forecast by the ECMWF to be over the Texas Panhandle is much weaker and faster in the GFS forecast. However, the short wave over the Southwest is essentially similar in both forecasts, although the GFS has considerably more small-scale structure and a more complex vorticity field. So, the exact timing and details of what will happen here is not well-defin, even for the short term.
The forecasts below are longer-term and are valid at 5 pm MST next Sunday, December 21st. The closed low forecast to be over the Southwest by then is slower and considerably stronger within the ECMWF forecast. The ECMWF forecast, were it to verify, would lead to a stormy, wet and cold day for us next Sunday. The ECMWF also forecasts a significant coastal storm to impact the middle Atlantic coast next Sunday; whereas, the GFS forecasts much higher heights and zonal flow over that region. So, considerable uncertainty about the details of the weather for much of country persists through the week - keep a close eye on things if you plan to be travelling next weekend.
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