Light Rain At Daybreak

It is raining lightly here in the north part of Tucson at daybreak, and there appears to be another 0.03" in the gauge - making the two-day total 0.65" so far. The NAM 500 mb analysis at 12 UTC this morning (15 December 2012) is shown below. The short wave that brought yesterday's rain and snow is now located about over Omaha. A broad trough continues over the Southwest, and there are two vorticity maxima analyzed by the NAM - one associated with the current light rain. The maximum near Las Vegas will keep the snow storm going over northern Arizona, where Flagstaff already has accumulated snowfall with a water equivalent of more than an inch.

The short wave over Omaha is associated with widespread precipitation over the western Great Lakes states. It seems a bit unusual that this mid-December storm is producing mostly rain. The only report I see of wintry weather on the 13 UTC surface plot (above) is an observation of freezing rain in eastern South Dakota. As the short wave moved over the High Plains yesterday, it produced a localized, December outbreak of severe thunderstorms centered in the Texas Panhandle (below) - with hail, wind and tornadoes. It looks like the active weather period over the western 2/3rds of country will continue through the coming week. The ECMWF spins up a serious blizzard that moves east out of Colorado during the second half of the week - currently 5 days away, but something to watch in coming model forecasts.

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