AccuWeather reports temperatures will surge over much of the eastern two-thirds of the nation this week into the weekend of Jan. 12-13, 2013, before the advance of arctic air.Steering winds, known as the jet stream, will retreat northward from the Rockies and Plains to the Midwest, South and mid-Atlantic.
Average temperatures are usually at their lowest point during this part of January. However, temperatures will trend to 10 to 20 degrees above normal during the warmup event. Places without snowcover will warm up the quickest.
The sun's energy will focus on melting the snow rather than warming the ground, where there is significant snowcover.
As the warmup progresses in much of the Central and Eastern states during this week, colder air will slowly dip southward along the West Coast. Cold air will try to hang on in New England and upstate New York during much of the week before a warmup takes hold toward this coming weekend.
Snowcover was at a 10-year record extent during the first few days of January, but will whither away from southwest to northeast. The fastest snow loss will occur in areas exposed to the sun and along paved areas.
Most ski resorts will retain a large amount of their base of snow. Most of trails are located on the north or shaded side of the mountain. In addition, man-made snow is more dense than natural snow, so that it melts at a slower rate when compared to natural snow.
The warmup may be deceiving in some locations and to some people. Long nights and episodes of clear skies and light winds will allow temperatures to drop substantially after dark.
In areas made wet by melting during the day, clear ice can form any time from the late afternoon into the early morning. Be especially careful when driving through wet areas as a result.
In most cases, the snowmelt will be gradual. However, a springlike storm with rain, severe thunderstorms and high relative humidity will drive northeastward through lower Mississippi Valley, into the Ohio Valley and then the central and eastern Great Lakes later in the week. As this happens, areas that have thick snowcover (lake-effect snow areas), could experience flooding problems.
The storm will deliver another dose of needed moisture from Texas and the southern Plains to the middle part of the Mississippi Valley.
During this weekend into week three of January, multiple waves of cold air will punch through the Rockies, Plains and Midwest. The waves will bring progressively colder and colder conditions.
"When you compare temperatures during the height of the warmup with the core of the arctic air that follows, some locations may have a difference of 40 degrees more," said Paul Pastelok, long range weather expert.
This is why AccuWeather.com is referring to the weather later in January as "brutal cold."
In the East, and especially the Southeast, the progression of cold will be delayed by multiple storm systems riding northeastward from the Gulf of Mexico and an area of high pressure trying to hang on until the very last.
The arctic cold is still forecast by AccuWeather.com's Long Range experts to break through to the Atlantic coast near or following the third weekend of January, provided one of the storms becomes strong enough to break down the high pressure area and draw the cold air in its wake.
EDITOR'S NOTE: This story was written by Alex Sosnowski, expert senior meteorologist for AccuWeather.com.