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Rain Event Update: Southeast U.S.

If you had a chance to listen to my weekly outlook you might have heard me mention the tightening thermal boundary over the Southeast U.S. in response to the negative Arctic Oscillation. Showers and thunderstorms have developed along this boundary with pockets of heavy rainfall.

The following image depicts radar, precipitable water (PW), and atmospheric pressure. A narrow band of showers and storms have formed along an axis of lower pressure and high PW. One-hour rainfall rates are nearing an inch in a few spots; however most hourly rates are closer to 0.25.”

This next image is an experimental short-term model showing total (15-hour) accumulated rainfall valid 12/11/2012 03Z. Based on this model, a narrow band (60 miles wide) of rainfall in the 1.0 – 1.5” range is likely from around Jackson MS to Huntsville AL to near Knoxville TN. Isolated amounts will near 2.0”

Flash flood guidance can provide some clues into the potential for runoff. 6-hour rates for most of this region exceed 2.5.” Thus, depending on the overall rate of accumulation, most, if not all, of this rain should soak into upper soils with minimal significant runoff.

Arctic Oscillation AO

I have been expecting a strongly negative AO to impact the nation’s weather through the middle of December. Well, it is here! Note today’s observation of the AO (red circle)—which is strongly negative. The image shows current national temperatures with blue/purple shades showing cold arctic air.

Heavy snow fell over the weekend across Minnesota and Wisconsin, as well as surrounding states. Sacred Heart MN reported 17.3” while Minneapolis reported 10.5” which was the 4th highest December total on record.