Wednesday, April 15, 2015

Rest Of Week Stormy Over Parts Of West

A cold, 500 mb low is centered just northeast of Salt Lake City this morning, with temperatures within the core of the system colder than -30 C. Although this system roared into the West yesterday, it is now forecast to take a somewhat long, strange trip before it exits onto the Plains. I show here a sequence of 500 mb forecasts from the 06 UTC run of the WRF-NAM at Atmo - times are in upper right corner and temperature color bar is at bottom. A trailing piece of the short wave digs south-southwestward, giving the system two circulation centers through much of the period covered here. By 0600 UTC on 18 April the closed low has only advanced to north-central New Mexico, with a strong vorticity maximum brushing through southeast Arizona late on the 17th.

Shown here are WRF-NAM precipitation forecasts for the period ending at 11:00 pm MST on the 17th. Precipitation produced by this system maximizes in Colorado, with the model forecasting a very significant event. Above is model's forecast of total precipitation, indicating the focus of the event over northeastern Colorado, north of the Palmer Divide. The model forecast of snowfall through the same period (below) indicates  maximum amounts of heavy snow remaining over the northern Foothills of the Rockies. Interestingly, the current morning forecasts from the Denver/Boulder NWS Office indicate a maximum precipitation probability of only 70% for both DIA airport and also west Ft. Collins on Thursday night - with snow accumulations of just 1/2 to 1 inch. Details of where the heavy, wet snow falls will be modulated by the surface to 500 mb temperature profiles - 500 mb temperatures of -30 C most always bring snow east of the Foothills, across the major megalopolis along the Front Range.

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