Thursday, December 01, 2011

Big Changes Have Arrived

The 500 mb NAM analysis from 12 UTC this morning (above) shows that, just as predicted by the global models for a number of days, a strong cutoff has moved south-southwestward across the Great Basin and is centered near Las Vegas. The system is quite powerful, with temperatures of -25C and colder at 500 mb. A 8 am MST surface plot for the Southwest is shown below. The surface low is centered over western Arizona with SLP below 1000 mb. The storm has produced strong winds through the night over much of the Southwest. Note also the strong cold front and snow that has plunged southward down the Front Range.

The Atmo early run of the WRF-GFS forecasts very strong low level winds locally during the day today - forecast above is valid at 8 am - forecast indicates 40 to 50 mph+ low-level jet right across Tucson metro area. We had a brief period of 30 to 35 mph winds here at the house during the past hour. The NAM precipitation forecast has now come in line with the earlier forecasts of the GFS. Accumulated precipitation precipitation forecast through next 48-hours is shown below. Winter has definitely arrived in the low desert as December begins.

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