The large 500 mb trough that is off the west coast this morning has a very complex structure, with a number of distinct short waves embedded within the larger-scale feature. One short wave is forecast by this morning's NAM to be ejected across the Great Basin today and tonight with little amplitude. Although precipitation covers most of California this morning, all the way south to San Diego, both the NAM and the WRF-GFS run at midnight last night forecast only a bit of precipitation in far northern Arizona. By the weekend however a much sharper trough is forecast to approach the Southwest, and this wave may bring enough moisture with it for a precipitation event across much of Arizona. (Note that February to date has been rain-free and almost cloud-free here in Tucson.) The top graphic shows total precipitation forecast by the Atmo version of the WRF-GFS for the period ending at 10 am Saturday morning (February 19th) and indicates a large band of rainfall and high elevation snowfall moving into southeast Arizona. The NAM however is slower (bottom graphic shows its prcipitation forecast for the 60 hours ending at 5 pm Saturday), and keeps the precipitation over northern portions of Arizona through early Saturday night. Regardless, finally a possible weather event for the Southwest!
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