What is a “nor’easter”?

Weather Blog

AUSTIN (KXAN) — Over the weekend, while we were enjoying sunny skies and pleasant temperatures here in Texas, New England was in the midst of the first nor’easter of fall/winter.

A nor’easter is a strong area of low pressure that usually forms within 100 miles off the East Coast between Georgia and Maine.

The counter-clockwise flow of the winds around the low as it travels up the coast are out of the northeast which is where the name derives from.

While these storms are often associated with heavy snow, it’s not necessarily required for such a storm. The main categorizations of a nor’easter are that the direction of the storm and direction of the winds be out of the northeast.

The heavily populated cities of the I-95 Northeast Megalopolis are most prone to these storms, as they can bring heavy rain, blizzard conditions, and coastal damage.

Nor’easters are strongest and most frequent between the months of September and April as the polar jet stream surges cold air south and eastward from the north pole. This cold air clashes with the warm, moist air of the Gulf of Mexico being transported northward by the Gulf Stream.

The Gulf Stream is a warm ocean current that generally runs parallel to the East Coast, keeping a near endless supply of relatively warm air throughout the winter months. This high contrast in temperatures from the cold land and warm oceans creates the instability needed for a nor’easter to thrive.

Additionally, the formation of a nor’easter is a result of cyclogenesis, meaning the development of an area of low pressure. As a low strengthens, the central pressure of a low will drop. If it drops 24 millibars or lower within a 24-hour time frame, it will “bomb out” and become a bomb cyclone.

Satellite image of the 1993 nor’easter.

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