A rapidly intensifying extratropical cyclone with a pressure drop of at least 24 millibars in 24 hours is commonly called a bomb cyclone. The meteorological process itself is known as explosive cyclogenesis or bombogenesis.
The “bomb” refers to the speed of the storm’s deepening, not to its shape or a particular type of precipitation. Falling central pressure usually means the cyclone is strengthening, tightening its pressure gradient and increasing its potential for powerful winds. These storms often develop where contrasting air masses and strong upper-level jet-stream dynamics reinforce rising motion near the low-pressure center.
The 24-millibar benchmark is the standard reference at roughly 60° latitude, but the formal threshold varies with latitude. Meteorologists use a latitude-adjusted version of the definition because the typical scale of atmospheric systems changes from the tropics toward the poles.
Bomb cyclones are extratropical, meaning they differ from tropical cyclones such as hurricanes. A nor’easter may become a bomb cyclone, but the terms are not synonyms: “nor’easter” describes a regional storm and wind pattern, while “bomb cyclone” describes exceptionally rapid pressure deepening.