Joe Lundberg

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Frontal Wave and Southern Branch Feature Give Qay to Quiet Pattern

January 15, 2013; 11:08 AM ET

Tuesday, 11:35 a.m.

Two disturbances will bring precipitation through the eastern third of the country in the next couple of days. Once the southern branch feature leaves the Carolinas Thursday night and early Friday morning, we'll be in a dry weather pattern that will last through the weekend. At that point, the biggest thing we'll have to look at will be the impending arctic outbreaks.

The first of these features is a frontal wave that is spreading clouds and mainly rain up through the northern Gulf Coast states into the central Appalachians, with a little ice over the northwest fringe of the precipitation. As this wave of low pressure moves steadily northeastward tonight, it will throw that moisture farther and farther north into a colder air mass. The cold air across Pennsylvania into New England is hardly deep, but it is deep enough for a couple of forms of wintry precipitation - snow and sleet. Where it is below freezing in most of the atmosphere, then we'll see snow. Where there is a warm layer aloft, then it will be more sleet.

That dividing line between all snow and mixed precipitation will get awfully close to Pittsburgh tonight, as well as to State College. It will easily end up north of New York City and could wind up north of Boston tomorrow. South of that line, any snow accumulations will be limited, and if you're living in south-central Pennsylvania and central and southern Jersey into the southern half of Connecticut, central and southern Rhode Island and all of southeastern Massachusetts, the cold air just won't be deep enough to warrant much snow.

On the other hand, where it is all snow, we could be looking at a solid 3 to 6 inches of the white stuff, with locally 8 inches in some of the higher ground from central and northeastern Pennsylvania into the northwest Hills of Connecticut and perhaps the Berkshires and the hills around Worcester. That will do well to replace the snow that was just wiped out by recent surge of very mild air.

The other system is more of an upper-level low rolling across Texas now. The latest runs of the NAM model have come around more to the other models that have been a little quicker with this feature coming eastward across the South, and the growing consensus is that it moves slowly but steadily across the lower Mississippi Valley tomorrow night then steadily accelerates across the rest of the South Thursday before exiting the Southeast coast Thursday night. There will be rain with this storm, a chilly rain, by and large, but it may not be all rain. In fact, snow is a real concern across northern parts of Mississippi, Alabama and Georgia as the storm rolls through. Most of the moisture will be restricted from reaching the Tennessee Valley to northern North Carolina and especially Virginia.

After that, it will get quiet for the most part. Then it's just a matter of timing the arctic outbreaks. Some arctic air will move into the Great Lakes later Thursday and Thursday night and into the Northeast Thursday night and Friday, but the core of the cold stays up across Ontario and Quebec.

As we have been touting since the latter stages of last week, though, much colder air will be building heading into the weekend, and a couple of cold fronts will pull that growing arctic air mass farther south with time. It looks like it drills into the Dakotas and Upper Midwest later this weekend and could well sweep to the Gulf Coast and East Coast by early next week.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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Joe Lundberg
Joe Lundberg, a veteran AccuWeather.com forecaster and meteorologist, covers both short and long-term U.S. weather on this blog.