Arctic Cold Fronts, Gulf Stream, & Nor'easters

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The storms discussed above occurred on the West Coast of the U.S., but what about similar storms that form on the East Coast? When similar storms form along the eastern seaboard, they can often grow into monster storm systems that have wide-ranging impacts. When they do develop, they are termed nor’easters. In most storm formation scenarios, warm moist air masses originating from the Gulf of Mexico move north and east. They then collide with cold fronts originating from Arctic Canada that push south. In many cases, the warm air masses form ridges of high pressure that form on either side of a cold air trough. When the air masses collide, low pressure develops as the warm air mass on the leading side of the trough is forced upward.

Like tropical cyclones, these storms can actually intensify when they are fueled by warm water. In the case of nor’easters, when the low-pressure system moves over the mid-Atlantic coast, they often intersect air masses fueled by the warm Gulf Stream. This warm water produces moisture-laden air that rises rapidly when displaced by the denser cold air and helps to strengthen the convective uplift. By pumping additional warm, moist air into the atmosphere, these storm systems can become stronger, often with gale force winds, and intensive precipitation. As most of these storms occur in the winter, they often result in significant snowfall inland and have intensive coastal impacts with high waves and intensive erosion. Each year, nor’easters can be relatively minor or can be very severe.

This video (2:30), What is a Nor'easter, helps explain how these types of storms form.

What is a Nor'Easter?

Click for transcript.

Hi, I'm meteorologist Rob Koch with you on weather nation covering an in-depth look – more at the Northeast storms, Nor'easters as they're known by. And, of course, we're dealing with one moving across areas of New England and parts of the Mid-Atlantic. Well, we're going to talk about how these systems form, by definition. We're also going to talk about, historically, how many we see each year. And the number may actually surprise you.

It is astonishing, but in the works we've got the cool air coming into this low-pressure trough. We've got the warm conveyor belt of air along the jet stream riding right over the top of the Gulf Stream, which is that warm puddle or pool of air that circulates through the Atlantic Ocean. So, by definition, a nor'easter is officially, it's a mid-latitude or extra-tropical cyclone that tracks along the US east coast or the Atlantic seaboard. The name of it comes from the fact that the wind direction in those coastal communities impacted by the storm is from the Northeast, thus the term nor'easter. No other reason why it picked up that name besides that.

Typically, we'll see these occur between the months of September and April. It can start as late as October, but will always go to typically around April. And they usually do develop over the Gulf Stream, originating around Georgia and up towards the New Jersey coast. Now, in an average year, in an average year, there can be as many as 20 to 40 Nor'easters in a year. That's an extremely high number. But of those, only about two to three actually become significantly severe. So that number, thankfully, is quite low.

So, here's usually the ingredients that need to come together. You need to have the cold air coming out of parts of eastern Canada. You also need to have the Labrador Current coming in from the north. Then you have the Gulf Stream meeting up. Cold air, warm air. Recipe is in the water. Well, that cold air - warm air starts to develop a low-pressure system, just like our latest system forms off the Carolina coast and then makes its way to the Northeast very quickly. And on its left side we see very heavy rainfall. Sometimes, if the air is cold enough, it'll be snow, very windy conditions. The worst weather tends to be on the west side of the storm and within about a 150 to 300 mile to the west of that track.

So again, this latest system moving on through is certainly going to be having an impact in the Northeast. That Gulf stream, still with water temperatures easily above 70 degrees, well offshore from the US East Coast.

I'm Rob Koch.

In this silent animation (0:45), Satellite View of February Nor'easter, produced by NASA’s Goddard Space Flight Center using NOAA’s GOES satellite, you can see how a nor’easter formed in February 2013 when New England and much of the U.S. Northeast was impacted by heavy snowfall, ice, and high winds. There is no narration with this animation.

Satellite view of February Nor'Easter

By carefully watching this video, you can follow water vapor that originates in the Gulf of Mexico and a series of cold fronts that move east from the central U.S. As this water vapor moves off the mid-Atlantic, the air masses collide and intensify into a well-organized counter-clockwise rotating low-pressure cell that brings much of the moisture at high altitude back over land from the northeast. As the center of circulation is located along the New Jersey coast, the rotation brings intensive winds out of the northeast to the New England coastline.