Storms · 5 min read

What Is a Nor'easter? The East Coast Storm Explained

By Emma Clarke · November 10, 2026

When forecasters on the East Coast talk about a nor'easter, people from Washington to Maine pay attention. These storms can bury cities in snow, flood coastal roads and knock out power for days. But what exactly is a nor'easter, why does it form along the coast, and what makes one storm a light rain and the next a blizzard?

Image: GOES East satellite view of the nor'easter of March 2, 2018, NOAA, Wikimedia Commons (public domain)

What is a nor'easter?

A nor'easter is a large low-pressure system that forms or strengthens along the East Coast of North America and moves up the coast toward New England and Atlantic Canada. The name comes from the wind: as the storm passes offshore, the counterclockwise flow around the low drives strong winds from the northeast, off the Atlantic and onto the coast. That onshore wind pushes water toward the shore and carries moisture from the ocean inland.

How does a nor'easter form?

The fuel for a nor'easter is contrast. In late fall and winter, cold air from Canada sits over the continent, while the Gulf Stream just off the coast stays relatively warm. Where the two meet, the atmosphere is primed for storms. When a dip in the jet stream moves over the East, it can help a low form near the Carolinas or the Mid-Atlantic coast, or pull a low from the Midwest toward the coast, where it strengthens over the warm water.

Some nor'easters deepen very quickly. When the central pressure of a storm drops by at least 24 millibars in 24 hours (at the latitude of New England), meteorologists call it bombogenesis, and the storm a "bomb cyclone". Not every nor'easter is a bomb cyclone, but the strongest ones often are.

Snow, rain, wind and flooding

What a nor'easter brings depends on the track and the temperature. If the storm stays offshore and cold air is in place, the coast can get heavy snow and blizzard conditions. If the storm tracks closer to the coast, or the air is milder, the big cities along I-95 get mostly rain, and the heavy snow falls inland and on higher ground, as in this week's storm, described in our news article on the Northeast cold blast. A shift of 50 to 100 miles in the track can make the difference between a few inches of slush and a foot of snow, which is why forecasts for nor'easters often stay uncertain until the last day or two.

Along the coast, the northeasterly wind piles water against the shore. Combined with high tide, that can cause coastal flooding and serious beach erosion, and because a nor'easter moves slowly, the wind can blow for several tide cycles in a row.

When is nor'easter season?

Nor'easters can form at any time of year, but they are most frequent and most intense between September and April, when the contrast between cold continental air and the warm ocean is greatest. Early-season nor'easters, in October and November, often bring more rain and wind than snow, because the ocean and the ground are still relatively warm. The big snowstorms usually come from December to March. Historic examples include the Blizzard of 1978 in New England, the "Perfect Storm" of late October 1991 and the March 1993 "Storm of the Century", which brought snow from the Gulf Coast to Maine.

Nor'easter vs. hurricane: what is the difference?

A hurricane is a tropical storm that forms over warm ocean water and draws its energy from that heat; its strongest winds are concentrated around a small eye. A nor'easter is a cold-season storm that gets its energy from the temperature contrast between air masses, along fronts, like the cold fronts and warm fronts on a weather map. A nor'easter is usually much larger than a hurricane, with strong winds spread over a wide area, and it brings snow as well as rain. Hurricanes get official names from the National Hurricane Center; nor'easters do not have official names in the US.

How to prepare for a nor'easter

Follow the forecast from your local National Weather Service office, because small changes in the track can change everything. If you live near the coast, know whether your area floods at high tide. Charge phones and have flashlights ready in case of power cuts, clear gutters and storm drains, and avoid driving in heavy snow or through flooded roads. For your city, check the 14-day forecast, and see what warning colors mean in our guide to weather warnings.

Frequently asked questions

What is a nor'easter?
A large low-pressure storm that forms or strengthens along the East Coast of North America, named after the strong northeasterly winds it brings in from the Atlantic.

When is nor'easter season?
Nor'easters can form at any time of year, but they are most frequent and strongest between September and April. Big snowstorms usually come from December to March.

What is the difference between a nor'easter and a hurricane?
A hurricane is a tropical storm that feeds on warm ocean water. A nor'easter is a cold-season storm that feeds on the contrast between cold and warm air, is usually much larger and can bring heavy snow.

What is a bomb cyclone?
A storm whose central pressure drops by at least 24 millibars in 24 hours, adjusted for latitude. The strongest nor'easters often deepen this fast.

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