Friday, April 08, 2011

Storm Digging South Along California Coast

Strong 500 mb cutoff is currently over central California and digging south. The system is already impacting northern Arizona - see top view looking north from NAU in Flagstaff toward the San Francisco Peaks, which are obscured in snow. The NCAR RAP 500 mb analysis for 12 UTC (bottom) shows unusually cold temperatures in the core of the system, with -35C, or a bit colder, observed this morning. The latest NAM forecasts indicate that a small pocket of 1000-500 mb thicknesses of 5340 m, or a tad lower, will move across southern Arizona tomorrow night - so snow levels will come down quite low for April.
The U of A Atmo version of the WRF-GFS model run at midnight is forecasting another event that would affect mainly higher elevations of southeastern Arizona (see top graphic below). Much like the last system I followed, only very light precipitation is forecast for the Tucson metro area, but a nice event at higher elevations of the Catalinas and Rincons. This morning's 12 UTC run of the NAM model forecasts more precipitation at lower elevations, with up to half an inch indicated for the metro area (bottom image below). Note that both of the forecasts below are for total precipitation for the period ending at 12 UTC on Sunday morning. The last event tracked like this turned out to produce actual precipitation that was about an average of the two models. So, we will watch to see how this event evolves - definitely a return to winter-like conditions, which will be a nice respite.

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