Millers To Maulers: Your Winter Storm Guide

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The term “nor’easter” is fairly common in winter weather vernacular and refers to strong areas of low pressure along the U.S. East Coast featuring winds from the northeast coming off the Atlantic Ocean.

These storms are typically associated with winter and snowstorms, and they’re most common and strongest between September and April. But nor’easters are actually possible year-round, as long as a low-pressure system fits the criteria.

Just like snowflakes, no two nor’easters are exactly alike, but they can be sorted into categories, named after the researcher who came up with the system in 1946, J.E. Miller.

The two types, Miller Type-A and Miller Type-B, are generally characterized by where the nor’easter forms, and therefore what path it takes.

Miller Type-A

The first Miller category includes nor’easters that primarily develop near the Gulf Coast or East Coast along an old cold front or the boundary between marine and land air masses.

These types of nor’easters are considered “classic” nor’easters.

As Miller Type-A nor’easters travel up the East Coast, inland areas and high elevations are likely to see snow while the precipitation type along the coast is more variable. If the storm is a bit farther east, cold air can get closer to the coast, increasing the chance of snow.

(MORE: Why Do Snowfall Forecasts Change as a Potential Storm Gets Closer?)

Cities like New York and Boston and the Interstate 95 corridor can have wildly different forecasts depending on the exact track of these systems.

The March 1993 “Superstorm” is one famous example of a Miller Type-A storm.

Miller Type-B

Miller Type-B nor’easters are a bit more willing to share the wintry love with inland areas than their coastal counterparts.

These systems approach the Northeast from the west, often through the Ohio Valley, bringing precipitation to the Midwest on their journey. As with Miller Type-A storms, there is a delineation between rain and snow, but this time it’s more of a north-south split, rather than an inland-coastal split.

Miller Type-B storms are also characterized by a brief identity crisis when the center of low pressure reaches the Appalachian Mountains.

The change in terrain causes the initial low-pressure system to weaken as the central pressure goes up, but this sets the stage for the low to redevelop on the eastern side of the mountain range. This process is also known as a “center-jump.”

Bonus Case: Alberta Clippers

Alberta clippers are another common type of winter storm, but they only sometimes fall into the category of a nor’easter.

(MORE: What Is An Alberta Clipper?)

An Alberta clipper is a fast-moving area of low pressure that moves southeastward out of the Canadian Province of Alberta, through the Plains and Midwest.

This type of winter storm qualifies as a nor’easter if it follows the path of a Miller Type-B storm, eventually reaching the East Coast and causing northeasterly winds coming off the Atlantic Ocean.

Sara Tonks is a content meteorologist with weather.com and has a bachelor’s and a master’s degree from Georgia Tech in Earth and Atmospheric Sciences along with a master’s degree from Unity Environmental University in Marine Science.