In the northeastern United States, nor’easters are well known for producing heavy precipitation, strong winds, and coastal flooding. Despite approaching the region from the south, they take their name from the steady northeasterly winds that blow in off the ocean.
Nor’easters can occur any time of the year but are most common between November and March. This is because the cold air that dips south in a jet stream trough during fall and winter often meets warmer air moving north over the Gulf Stream, which is just off the east coast. This contrast in temperature strengthens the storms. That said, there are a few different ways in which they can develop.
The first is called a “Miller Type-A” storm and is considered the “classic” nor’easter. These occur when an area of low pressure develops along the Gulf Coast or Atlantic Coast and intensifies as it tracks northward along the eastern seaboard.
The second type originates in the mid-west and is known as a “Miller Type-B” storm. Traveling east, these low-pressure systems weaken when they run into the Appalachian Mountains and transfer their energy to the coast. Often called a “center jump”, this transfer strengthens or creates a secondary low on the lee side of the mountains, which then moves northward. These types of storms are notoriously difficult to forecast as everything depends on the timing and location of the energy transfer between the two lows.
Both Miller “types” are named after James E. Miller, an atmospheric scientist who studied storm formation in the Atlantic coastal region during the mid 20th century.
Typical Miller Type A and B storm tracks. Credit: NOAA