Wednesday, January 09, 2013

Next Short Wave Off Northwest US

Above image is of water vapor in the upper troposphere at 14 UTC this morning (Wednesday, January 9th). The next short wave to affect the Southwest is off the the coast of the northwestern US and western Canada.     This feature is forecast by the models to dig into the Southwest and bring a strong cold front with it (front passes the Tucson area around midnight on Thursday night). The water vapor image seems to indicate that this system has a nice link with subtropical moisture from east of Hawaii. However, the 13 UTC eastern Pacific MIMIC-TPW product from CIMSS, at the University of Wisconsin, (below) indicates only a weak plume of higher PW currently with the system, indicating mostly middle-to-high level moisture and clouds. This system seems somewhat like the last two in that it has trouble bringing moisture (at least in the nodel forecasts) through the large, very dry area west of Baja.

This morning's forecast of Atmo's high-resolution, WRF-GFS model forecasts another light precipitation event - above is total precipitation for the period ending at 5 am MST Friday morning. The surface plot forecast from WRF-GFS valid at 11 pm tomorrow night (below) indicates the front, with light showers, approaching the Tucson metro area. The forecast sweeps the front across all of the metro area by midnight.

As substantial ridging occurs over the Gulf of Alaska from the 10th through the 14th, several  more short waves/vorticity maxima dig down the east side of the ridge into the Southwest. These all are very cold, with low thickness values, meaning that any showers they might generate would bring snow to low elevations in southeast Arizona - something to keep an eye on.

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