Sunday, January 30, 2011

Huge winter storm this week - what are the impacts on the Mid-South?

The 24-hour news and weather channels are all abuzz about the "Groundhog's Day Storm" of 2011, which could adversely impact up to 100 million people, according to Accuweather.  Truth be told, it's more than just a Groundhog's Day storm.  This monster system will impact locations across the Plains tomorrow with snow, while ice accumulation will begin across the Heartland from St. Louis east to Cleveland. Tuesday looks to be the biggest impact day as the storm system sweeps quickly across the Midwest into the Northeast.  Ice accumulations of 1/2" or more are likely just north of the Ohio River, affecting places like St. Louis, Indianapolis, and Columbus, OH, while significant ice is also likely in Cleveland, Pittsburgh, Philadelphia, and into the NYC metro.  That will be followed by potentially heavy snow on top of the ice, as well as places further north like Chicago, Detroit, Toronto, and much of New England.  The map below is courtesy of Accuweather.

So what about the Mid-South, since that IS what specializes in? While last week the storm track appeared to be slighty further south, fortunately most models have narrowed in on a track that takes the low pressure system from eastern TX across the Mid-South (just north of the metro area) into Kentucky. Given all of the weather types that will exist for this storm, that is probably the best track it can take for us. The major wintry precipitation will be to our north and the highest potential for thunderstorms will be to our south.

Our main concerns will be the possibility of flash flooding due to heavy rain on Tuesday and high wind, also on Tuesday afternoon and evening. A changeover to light wintry precip will still be possible early Wednesday though. The maps below show a few different computer models and their respective forecast positions of the surface low pressure at 6pm Tuesday.  The European, GFS, and NAM all have a similar track with the European lightly more progressive (faster) than the U.S. based models.  The Canadian model seems to be a northern outlier, taking the low over southern IL Tuesday evening.

00Z ECMWF (European) model forecast at 6pm Tuesday - low pressure over western KY

12Z Canadian GEM model forecast at 6pm Tuesday - Low pressure over southern IL

12Z GFS Model forecast at 6pm Tuesday - low pressure over northeastern AR

12Z NAM forecast model at 6pm Tuesday - low pressure just north of Memphis
You can see that heavy rain is forecast with this system (perhaps 1-2" on Tuesday) and the tightly-packed isobars (concentric circular lines around the low) indicate that there will also be quite a bit of wind at the surface.  In fact, the wind just ahead of the low at about 5,000 feet could reach 75-80 mph!  If any of that wind were to be transported to the surface by downdrafts from thunderstorms, it wouldn't be hard to get a severe storm with damaging straight line wind.  On average, surface wind will likely gust from 30-40mph Tuesday afternoon and evening.

As the low passes by, temperatures will plummet.  Early indications are that it will be near 60 just ahead of the cold front (about 6pm Tuesday) and could fall to near 30 by midnight!  Any lingering precipitation could changeover to wintry precipitation late Tuesday evening, but I expect everything to move out quickly - by early Wednesday - as the storm races into the Ohio Valley. will continue to keep you apprised of the expected conditions and any changes to the forecast.  Follow this blog, Facebook, Twitter, and the main website for updates the next couple of days.

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