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© Weather Channel
Winter Storm Alerts
We are watching for a potentially major winter storm to affect a long swath of the Deep South this week - including places better known for their beaches, balmy breezes and hurricanes. This will include some of the areas affected by Winter Storm Kronos just last week - but it includes millions of people farther east as well.

The threat stems from the combination of a bitterly cold arctic air mass plunging southward behind a sharp cold front, while moisture streams northward from the Gulf Coast. As the moisture crosses into the cold air behind the front, a swath of frozen and freezing precipitation is likely to break out.

The National Weather Service has issued winter storm watches, warnings and advisories from southeast Texas eastward along the Gulf Coast through Georgia, the southern half of South Carolina, eastern North Carolina and far southeast Virginia. For Charleston, S.C. and Savannah, Ga., it's the first winter storm watch issued for those two cities since Feb. 11, 2010. For Houston, it's the second time with a winter storm watch in just five days.

Let's step through the forecast and get into the details and uncertainties.

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© Weather Channel
Tuesday Forecast
Long Stretch of Ice and Snow

The latest blast of arctic air, already bursting south into the Midwest, will reach the Deep South Monday night. Temperatures should be at or below freezing by Tuesday morning along the Gulf Coast from Houston to Pensacola, Fla., as well as portions of the Carolina coast.

As Tuesday wears on, a broad zone of rising air will develop across the entire Gulf Coast (except for southwest Florida) and the Atlantic Coast of the Southeast, along and behind the arctic cold front. This will allow an elongated area of precipitation to develop from South Texas all the way to the Carolinas.

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© Weather Channel
Tuesday Night Forecast
Since much of this precipitation will be falling over areas where near-ground temperatures will hover below freezing, the result will be a mess of wintry precipitation.

Exactly which form the precipitation takes will depend on temperatures several thousand feet aloft. In some areas, the entire atmosphere will be below freezing, and those areas will be vulnerable to snow. In areas closer to the Gulf Coast, there is likely to be a layer of above-freezing air above the ground, setting the stage for sleet and/or freezing rain.

But model projections disagree on exactly how far south the all-snow scenario will get - not just Tuesday, but for the duration of the storm.
For that matter, it is not entirely clear just how far north (inland) the wintry
precipitation will fall. More on that later.

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© Weather Channel
Wednesday Forecast
By Tuesday night, as an upper-air disturbance moves into the western Gulf of Mexico and a separate area of weak low pressure develops off the Carolina coast, we expect areas of heavier precipitation to break out from the central Gulf Coast to the Carolinas. This will bring the potential for heavier snowfall and/or ice accumulation in these areas, again depending on the precise vertical temperature profile in the atmosphere.

Precipitation should end west of the Florida Panhandle by Wednesday morning, but Wednesday will see precipitation lingering from central and northern Florida to southeast Virginia. While wintry precipitation will probably stay north of the Florida/Georgia border (though not by far), leaving the Florida Peninsula just wet, there could be additional snow and ice accumulations from south Georgia northeastward.

Where, How Much, and How Bad?

Forecasting snow and ice accumulations in the Deep South is, as you might expect, always tricky.

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© Weather Channel
Significant Icing
There are two main factors contributing to the uncertainty this time:
  • How far south will the entire atmosphere be below freezing, allowing for pure snow?
  • How far inland will the precipitation fall?
Computer models continue to differ on the exact placement of the heaviest snow and ice accumulations.

This does appear to be a fairly moisture-loaded system for areas along the coasts, so snow and ice accumulations could be quite heavy, particularly from central and south Georgia to the eastern Carolinas.

Greatest Icing Threat:
Right now, it appears the most significant icing is possible from southeast Louisiana to south Alabama, south Georgia and coastal South Carolina. This could lead to falling limbs, trees, and significant power outages.

Greatest Snow Threat:
The greatest chance of significant snow accumulations at this time appears to line up from central Georgia into central South Carolina, eastern North Carolina and far southeast Virginia. If the precipitation falls as all snow and does not mix with sleet, amounts of up to 6 inches or more are within reach.

The threat of icing and a few inches of snow or sleet will also extend westward into southern Mississippi, Louisiana and southeast Texas.

Regardless of the precipitation type and amounts, very hazardous travel is likely across a long swath of the South from southeast Texas to southern Louisiana, southern Mississippi, southern Alabama, central and southern Georgia, South Carolina and eastern North Carolina in the Tuesday to Wednesday timeframe.

As for the second question, it currently appears that accumulating wintry precipitation will mainly stay south of the Interstate 20 corridor from Dallas-Fort Worth to the Mississippi River, missing cities such as Shreveport, La. The scenario is more iffy farther east, with a chance of light snow accumulations for Jackson, Miss.; Birmingham, Ala.; and Atlanta. Some computer models bring light snow accumulations all the way into the northern Atlanta suburbs. Still, there remains a chance that those areas will see nothing, and the more likely zone for accumulating snow and ice remains south of those cities.

As with any Deep South winter storm, additional complicating factors include warm ground (high temperatures in the 50s, 60s and 70s Monday) as well as the amount of precipitation that falls and what form it takes.

Prepare Now

This storm has the potential to disrupt travel and power. There is uncertainty on the amount of wintry precipitation that will fall. However, if ice accumulations reach the higher end of the range of possibilities, there could be widespread power outages and road blockages due to falling trees and tree limbs, not to mention the weight of ice on power lines themselves.

Travel could become dangerous or even impossible in some areas due to heavy buildup of ice and/or snow.

Our WeatherReady winter weather safety section has more tips on how to prepare for the possibility of dangerous driving conditions and extended power outages.