That dusting or so of snow that you woke up to Sunday morning across much of the area is nothing compared to what is expected in the Northeast this week. But that "storm" that brought the dusting is the SAME storm that will unleash a beastly blizzard in the Northeast. How is this possible?
This Alberta Clipper came out of the gates stronger than originally forecast. Because of this, and some fluid dynamics mumbo jumbo that I won't bore you with, the wave ended up moving through the Upper Midwest a couple hundred miles further to the west, digging deeper than most clippers do. This dive allowed it to pick up more moisture from the Gulf of Mexico as it made its way through the Ohio Valley and Carolinas. Then, it did something that 99% of clippers never do; it hit the Gulf Stream. This is like lighting a match in a forest that hasn't seen rain in years. The storm explodes with an almost endless supply of fuel (heat and moisture from the ocean) and enough cold air already locked in place to produce snow instead of rain. Combine this with a ridge behind it, which prevents another storm from pushing it along faster, and a reasonably strong high pressure in southeast Canada also preventing it from picking up speed, and you have the recipe for one very large blizzard. Let me show you….
So the clipper moved through the Upper Midwest over the weekend as seen in this vorticity image below. Vorticity is basically a fancy word for spin in the atmosphere. Remember that all of our storms have a large scale counter clockwise spin to them because of the Coriolis Effect. It is also considered a weak wave because it is open…. Meaning that the lines of equal pressure don't form a circle (called a closed low in weather terms).
The wave digs much deeper south than almost every other clipper on Monday allowing it to set up shop just off the coast of North Carolina…. But it's still not a closed low.
Here it interacts with the heat and moisture from the Gulf Stream, that river of very warm water located in the western Atlantic that stretches from the Gulf of Mexico all the way to the U.K. This picture was taken from Google images of the warm waters in May of 2006.