This time of year we begin to think about strong storm systems becoming Nor’easters. Actually, from fall to spring Nor’easters are a potential threat for the U.S. East Coast. All that’s needed is a strong, cold storm system to reach the warm Gulf Stream current. In true Nor’easter fashion, a winter storm (or, in this case, pre-winter storm) can just explode when it reaches the Gulf Stream off the Mid-Atlantic Coast as the contrast in temperatures (cold storm, warm waters) allows the bottom to fall out of the low and central pressures to plummet. From there, and if the upper flow is right, the strengthening low is then driven up the coast effecting every place from the Outer Banks of North Carolina to Cape Cod, to Nova Scotia, to Newfoundland with battering winds, torrential rain and — if cold enough — blizzard conditions.

February 24, 2010: The center of a Nor'easter sits just off the coast of New England. This storm brought two to three feet of snow from New England to interior New York to Pennsylvania and as much as four inches of rain to coastal New England.

Early last week Fred Schmude and I produced a winter outlook video that examined the possibility of a Nor’easter during the second half of December. Today’s the 15th — how’s it look? Actually, there is some potential. Let me clarify: The potential for a strong Atlantic storm system is high beginning early next week. However, will it pound the Atlantic Coast in true Nor’easter fashion?

Perhaps not. At least, perhaps not most of the coast.

First, the upper-level flow is in the right place to drive a strengthening storm from the Plains or the Great Lakes to the Southeast and then to the warm Gulf Stream, but the flow doesn’t quite look like it will keep the storm near the coast. Although there are early signs that our “locked” upper pattern is beginning to break down over the North Atlantic, this would only allow a developing Nor’easter to push farther out to sea (at least, initially).

Similar to a long-range hurricane forecast or, really, any long-range forecast, this scenario will likely change — several times! — before next week. The level of forecast uncertainty remains high. For now, strong storm? Yes. A Nor’easter battering the U.S. Coast? No…for all but the most northern regions. It does indeed look like the developing storm will not be directed completely out to sea. As we can see in the GFS computer model images for next Sunday, Monday and Tuesday, Maine, New Brunswick, Nova Scotia and Newfoundland should begin preparing for a battering storm.

As mentioned above, the currently high degree of uncertainty means nearly anything is possible. Perhaps one thing is certain: New Englanders and Canadians should get holiday shopping finished this weekend and have “just in case” storm supplies topped off and ready to go — the winter of 2010-2011 is just getting started.

Who else should prepare? Residents of the Southeast and the Appalachians should prepare for heavy rainfall and potential flooding as the this storm moves across Georgia Friday and reaches Jacksonville, Florida by Saturday before pushing offshore.

YourWeatherBlog has written about Nor’easters before. Some of the greatest East Coast blizzards of all time have been driven by Nor’easters and you can read about them here.

The StormWatch "Day 4" (Saturday) map shows the low centered over northeastern Florida with heavy rains pushing into the Southeast. Image: ImpactWeather StormWatch.

Sunday's GFS model shows the low well off the coast of Cape Cod with central pressure of 1005 millibars.

Monday's GFS now shows the low south of Nova Scotia and dropping pressure. As the pressure drops the contrast between the central low pressure and surrounding high pressure becomes greater allowing for a stronger storm with more damaging winds and perhaps record-breaking precipitation, as well as more far-reaching effects.

Tuesday's GFS shows the low pushing inland on the Maine/New Brunswick border. Central pressure remains strong at 982 millibars. The tight, concentric circles around the low indicate very strong winds while the darker greens indicate areas of highest precipitation.