Late-Week Snowstorm to Dip into the South

By Alex Sosnowski, Expert Senior Meteorologist

January 23,2013; 7:39PM,EST

The combination of lingering arctic air and two merging storms has the potential to spread a large swath of snow, wintry mix and slippery travel from the Midwest to the part of the South and Atlantic Coast at the end of the week.
As with many winter storms, it's complicated.
The storm scenario continues to trend colder and farther south than indications to start this week.
How much snow falls depends on how quickly two storms come together. One storm is coming from western Canada (an Alberta Clipper), and the other is a storm from the southern United States.

Midwest
Part of the Upper Midwest will be solely under the influence of the Alberta Clipper.
A broad area of snow and flurries will occur from around the Ohio River northward to the Great Lakes with coating to an inch of snow. Chicago, Louisville, Indianapolis, Cincinnati and Detroit fall within this area.
Part of this area could find a way into a heavier band of snow that brings a few inches. This is a little more likely farther east in Ohio, West Virginia and southwestern Pennsylvania, while areas farther west are more likely to have issues with dry air limiting the precipitation. Little or no precipitation is likely around St. Louis, but even a light amount of sleet or freezing rain can cause slippery travel.
A wintry mix and slippery conditions are likely from southwestern Kentucky to middle Tennessee including the Paducah, Ky. and Nashville, Tenn. areas.
Mid-Atlantic and the South
Farther east, the area from the northern Shenandoah Valley to Washington, D.C., Philadelphia, Atlantic City, N.J., and Dover, Del. northward to upstate New York, lie in a swath where it is a snow or no situation like that of the Ohio Valley states.

The same pockets of dry air from the Midwest could continue in between both the Alberta Clipper and the southern storm. As a result accumulations over much of this large area will range from a dusting in spots to a few inches of dry, powdery snow.

Colder air will have been around for a few days ahead of the late-week storm. As a result, the snow and wintry mix has a greater potential to adhere to paved and concrete surfaces, raising the risk of slippery conditions and travel delays.

It appears that farther south, a wedge of cold air will lead to snow and a wintry mix into northern and western North Carolina to a large part of southeastern Virginia and the southern Delmarva Peninsula. This includes the cities of Beckley, W.Va., Greensboro, Charlotte and Raleigh, N.C., Roanoke and Richmond, Va., and Salisbury, Md. Accumulations in this area would range from a slippery coating due to an icy mix to several inches of snow.
New York City, New England
Odds favor, cold dry air winning out around New York City and interior New England. It is possible that enough moisture from one or the other of the two storms produces a band of light snow in the area.
Southeastern New England (Cape Cod) is likely to share the same fate as New York City, unless the storms get together quickly and turn northward at the last minute. The more likely scenario being radar snow and a spotty light accumulation. The other outlier being an all-out blizzard.

A sneaky streak of snow could bring a coating to an inch of snow from Indianapolis, Ind. and Dayton, Ohio Wednesday to Washington, D.C. and Dover, Del., late Wednesday night into Thursday morning.

Forecast Challenges
Just as the chance that the western Canada and southern U.S. storms may fail to come together, leaving spotty light snow from the Ohio Valley to the East, there is still the potential the two late-week storms to fully merge.

The latter would produce a swath of heavy snow over part of the South and farther north over the mid-Atlantic and southern New England.
Because of the extend of arctic air, it will not take a great deal of moisture to produce several inches of snow. In this case a tenth of an inch of liquid (rain) could yield 3 inches of snow. A typical liquid to snow equivalent for storms in the East is 10 to 1, where a tenth of an inch of water would yield an inch of snow or an inch of water would yield 10 inches of snow.

The arctic air has already unleashed locally heavy lake-effect snow even in areas missed by the path of the general storms this week.

The dense arctic air is playing a major role in driving the storms farther south.

AccuWeather.com will have further updates on the potential for snow as the week progresses. Remember to refresh your browser as we will be doing live edits within this story.