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They are the biggest snowmakers for the East Coast and can paralyze the major Interstate 95 cities, but what triggers a Nor’easter to develop? Also, did you know there are two types of Nor’easters that bring heavy snow to the East?

Simply put, a Nor’easter is a Northeast winter storm. It’s a low pressure that powers up the East Coast and produces whiteout conditions on its western flank that can dump feet of snow. The question is…what weather pattern is favorable for these East Coast storms and when during the winter are they most likely to strike? Let’s answer these questions so you can be prepared the next time the television meteorologist exclaims during the newscast, “A Nor’easter is set to bring us heavy snow.”

An East Coast winter storm occurs when the jet stream or zone of upper-level winds splits in the West and rejoins in the East. What is meant by this? The polar jet stream, responsible for transporting cold air needs to drop or dip into the East. The southern branch of the jet stream, responsible for transporting moisture, should be focused from the Desert Southwest to the Gulf Coast and then turn northeast across Virginia and rejoin the Polar Jet Stream over Newfoundland.

This configuration of the jet stream allows the two jet streams to clash between the Mississippi Valley and southern Appalachians and a low pressure center to develop. The low pressure then moves either along the Interstate 95 corridor, parallels the coast or stays just off the coast as it pushes north from the Carolinas to New England. The exact track of the low pressure will determine where the heaviest snow occurs. In general, the heaviest accumulation is in a narrow 50-mile corridor about 150 miles west of the low pressure center.

Therefore, a storm track along Interstate 95 would bring the interior Appalachians to the Interstate 79 corridor, Upstate New York into the northern Green and White Mountains the heaviest accumulation. The surge of southerly air near and east of the storm center would allow snow to change to sleet, freezing rain and likely rain along Interstate 95. The zone in between would likely see a wintry mix of snow, sleet and freezing rain.

A storm track right along the coast would put the sweet spot for the heaviest snow accumulation along and just east of the Blue Ridge Mountains to the Lehigh Valley into central New England, including Albany, N.Y. Meanwhile, a storm track about 100 miles off the coast would place the entire Mid-Atlantic to New England coastline to Interstate 95 most at risk for heavy snowfall.

In a typical Nor’easter, the heaviest snow accumulation is 6 to 12 inches, but obviously the more intense storms can produce several feet of snow. While a narrow zone near the storm’s center produces a wintry mix, Nor’easters are not known for producing significant ice storms. There is usually a fast transition from snow to sleet, freezing rain and rain near and east of the low pressure’s track. This prohibits a prolonged period of freezing rain from accumulating heavy ice on trees.

Additionally, there are two types of Nor’easters. The most common type of Nor’easter develops a low pressure over the Gulf Coast and tracks north and east either along Interstate 95, the coast or parallel to the coast but out to sea. This type of Nor’easter produces a swath of snow from the Carolinas to New England.

The second type of Nor’easter originates from the Upper Midwest, dives south into the central Appalachians before transferring its energy to a coastal storm off the North Carolina coast and then sweeps along the Mid-Atlantic and Northeast coast. This storm track cuts off the southern Appalachians from seeing any precipitation and often leaves a void of significant snow accumulation along the highest peaks of the central Appalachians. The heaviest snow typically is focused from Pennsylvania’s Interstate 81 corridor to interior New England west of Interstate 95.

Like a hurricane, Nor’easters are known for producing coastal flooding thanks to the storm surge from the strong easterly wind component coming off the Atlantic. The beaches from the Mid-Atlantic to New England are susceptible to coastal flooding as the low pressure swirls up the coast.

When during the winter is a Nor’easters most likely to develop? In order of occurrence, February ranks the highest, followed by January, March and then December.

Believe it or not, Nor’easters are ranked on a special scale called the Northeast Snowfall Impact Scale. It was developed in 2004 and ranks Nor’easters based on the snow amounts and the number of people living in the storm’s path. The highest ranked Nor’easter so far is the Storm of the Century or Blizzard of 1993. In more recent times, the January 2016 blizzard is ranked fourth highest overall and was given the description of “Crippling.”

Knowing which Nor’easter type is expected and the track of the storm can help you better assess the risk for heavy snow, wintry mix or plain old-fashioned rain for your area!
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Story Image: A 1992 Toyota Tercel is partially dug out after the Superstorm of 1993 at Fort Devens, Mass. (Courtesy of Wikimedia Commons)

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Nor'easters: Closer Look At These Monster East Coast Storms