We've had different phrases to talk about specific types of winter storms long before the "polar vortex" became the media's go-to scapegoat for all things snowy and cold. The most well-known type of winter storm is a "nor'easter." Another big winter term is an "Alberta Clipper," and you're going to hear a lot about them this week.
An Alberta Clipper is a small, fast-moving low pressure system that originates in south-central Canada—sometimes in Alberta, hence the name—and races southeast towards the Atlantic seaboard. Since these clippers are small and somewhat localized systems, they have limited amounts of moisture to work with and only produce a few inches of snow on most occasions. Every once and a while, a surge of moisture from the south can work its way into the system, allowing the storm to overperform and produce snowfall amounts pushing double-digits.
Minneapolis, Chicago, Pittsburgh, and Washington D.C. are the biggest cities that are most commonly affected by Alberta Clippers. The latter is especially vulnerable to the quick inch or two these systems can produce—the snow day debacle seen in northern Virginia a few weeks ago was the result of snow from a clipper.
Thanks to zonal flow over the United States—a mostly east-west oriented jet stream without much of the troughing or ridging that produces active weather—the biggest weather story this week east of the Rockies will be these clippers. These systems will have to fight against warmer-than-average temperatures and uncertain levels of moisture in order to produce accumulating snowfall, but it looks like some areas—especially north of the Ohio River—will see a nice blanket of snow before next weekend.
Let's take a look at this week's storms, starting with the one tomorrow.
Here's a look at this morning's run of the GFS model showing sea level pressure (contours, in millibars) and six-hour precipitation amounts for 12:00 PM CST on Tuesday. The first clipper will swing through the Upper Midwest and Ohio Valley during the day on Tuesday, possibly bringing some rain and snow showers to the area as it scoots towards the coast. Disruptive snowfall accumulations are unlikely.
The second clipper system, which will join up with the first, is still hanging back in the Dakotas in the above model image. Each system will move towards the Mid-Atlantic in a hurry on Tuesday night.
Things start to get a little trickier on Wednesday afternoon. The GFS model thinks that Tuesday's clipper will begin to get its act together off the Mid-Atlantic coast just as the second clipper starts to approach the Appalachian Mountains. The enhanced lift from the two systems will likely produce a shield of precipitation across the Ohio Valley and Mid-Atlantic, with the heaviest precipitation likely from I-95 to the east.
If you look at predicted snowfall totals from the GFS model over the same period, while it's likely overdone in many locations, you can easily see the track of the clippers by watching the swath of snow grow from North Dakota to Pennsylvania.
The models show a third, well-developed clipper speeding down from the Dakotas towards the southeast early next week, but details are too sparse and the storm too far out to mention with any specifics at this point.
The East Coast isn't out of the woods just yet, though. We're heading into an active period of weather that coincides with cold air, which means an increased potential for snowstorms as February nears. Most of the models show a significant low pressure system developing in the Gulf of Mexico over the weekend and moving perilously close to the East Coast next week. Depending on the track of the storm, some areas could need to stand guard for the potential of a winter storm. It'll be a close one, and the possible storm is worth special attention as we get closer to the weekend.