What is a nor'easter? How they form and what to expect

The word "nor'easter" often brings to mind images of buried cars, blizzard conditions, and empty grocery store shelves. But what actually makes a storm a nor'easter?

Defining a nor'easter

What we know:

Despite popular belief, snow is not a requirement for a nor'easter.

A storm earns the title of "nor'easter" based on wind direction. If a strong low-pressure system off the Atlantic Ocean brings winds that blow from the northeast onto the coast, it's a nor'easter. If those winds are coming out of the east or southeast, it technically misses the definition—even if the impacts on land feel exactly the same.

Therefore, you can have a powerful nor'easter when temperatures are in the 50s. Instead of a blizzard, the region will just get battered by heavy rain and wind.

While they can happen at any time of year, nor'easters are most likely to occur between September and April, when the jet stream is stronger and more active.

Rain or snow?

Timeline:

If a nor'easter is brewing, millions along the East Coast will want to know one thing: Are we getting rain or snow?

Meteorologists look to a specific set of coordinates known as the "benchmark" (40 degrees north, 70 degrees west) to find out.

• If the storm tracks through the benchmark, it stays far enough off the coast to keep the freezing air locked in place over land, while still throwing immense amounts of moisture into the region. This is the classic recipe for heavy snowfall.
• If the storm tracks closer to the coast, it drags that warm ocean air inland, which changes the precipitation over to rain.

Two types of nor’easters

Dig deeper:

Meteorologists generally classify these storms into two distinct categories based on where they originate:

• Miller Type-A: This "classic" nor'easter develops along the Gulf Coast or the southern East Coast and tracks directly north-east up the Eastern Seaboard.
• Miller Type-B: This storm actually originates in the Midwest. As it moves east toward the Appalachian Mountains, it loses its organized center. However, once it crosses the mountains and hits the coast, it redevelops into a new low-pressure center and tracks up the coastline just like a Type-A storm.

Severe impacts

Why you should care:

Since nor'easters develop within 100 miles of the coast and typically reach their maximum intensity near New England, the heavily populated I-95 corridor takes the brunt of the damage.

These storms bring a dangerous mix of elements:

• Blizzard conditions: When snow mixes with 50+ mph winds, visibility drops to zero.
• Coastal flooding and beach erosion: Tropical-storm-force winds push massive ocean waves onshore. If a nor'easter stalls off the coast, the prolonged flooding can cause extreme damage that takes years to recover from.
• Widespread disruption: Because they target major travel and shipping hubs like New York City, Philadelphia, and Boston, a major nor'easter impacts the entire country's supply chain and travel network.