Monday, December 24, 2012

Christmas Eve winter weather discussion

We've posted daily blogs since last Friday on the chance of winter weather in the Mid-South. Today's post provides the latest information based on the morning computer model runs.

Christmas Day

Christmas Day will be wet - very wet - especially after Christmas lunch.  Rain moves in by noon or so with temps in the mid 40s and a gusty northeast wind. As low pressure moves into north MS in the evening, a warm front will approach the TN-MS border, which could put southeast portions of the metro (over north MS) in the warm sector of the system.  Strong storms are possible in this warm sector so some lightning and thunder will be possible for DeSoto, Marshall, Tate, and Tunica Counties, while the rest of the metro could see heavy rain.

Christmas Night

Once the low moves to our east, by late evening, wind will switch to the northwest and the arrival of cold air begins. As temperatures drop, especially across east AR, rain will change to snow overnight. Computer models indicate that there will be a tight gradient between the "haves" and "have-nots" as far as snow is concerned.  In fact, the morning GFS model snow output (below) indicates that the Mississippi  River will approximate the dividing line. Light amounts of snow (generally less than 2" and probably less than 1") will be found east of the river, while amounts of 6"+ could be found as close by as far northwest Crittenden Co.

6am GFS model output showing projected snow totals. A foot or more is possible around Jonesboro, while Memphis may see as little as an inch.
Not shown, the morning NAM model also placed heavy snow over the Little Rock to Jonesboro corridor, but had substantially less (1-2") for areas between Jonesboro and Memphis.  The ECMWF (Euro) model from last night was "middle of the road" with heavy snow over the same areas as the GFS and 1-2" in the Memphis metro.

What to expect in Memphis

So, specifically for Memphis and points east and south within the metro, the changeover will likely occur well after midnight, which would likely result in an inch, or perhaps less, of snow accumulation by dawn and flurries throughout the morning on Wednesday.  Roads will be passable and likely just wet as air temperatures should stay just above freezing Tuesday night and Wednesday morning east of the river and for most of the metro.  Temperatures on Wednesday will remain in the 30s with a gusty north wind, making it feel like the 20s all day.

Travelers warning

Across the river in AR, anything is possible, including enough snow to create hazardous driving conditions Tuesday night into Wednesday.  If you have travel plans into OK, AR (especially north of I-40), southeast MO, western KY and southern IL and IN, please consider the forecast conditions.  All of these areas could experience enough snow and wind to make travel treacherous.

Also note that areas from east TX through Louisiana, central and southern MS, and Alabama east into the Atlanta area are expecting a severe weather outbreak Christmas Day into early Wednesday morning.  Tornadoes, some of which could be strong and long-tracked, large hail, and damaging straight line wind are all possible. Storms will start in Louisiana and east TX tonight and move into MS by afternoon/evening and AL after dark Christmas night.  If you are traveling south, or have friends and family in these areas, PLEASE alert them to keep a close eye on the weather and monitor local authorities for the latest information.

Severe weather probabilities for Christmas Day/night. A severe weather outbreak is forecast for the Deep South.

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