Bombagenesis, a popular term used by meteorologists, occurs when a cyclone of medium latitude intensifies rapidly, dropping at least 24 millibars for 24 hours. A millibar measures the atmospheric pressure. This can happen when a mass of cold air collides with a mass of hot air, like air over the warm waters of the ocean. The formation of this rapidly strengthening meteorological system is a process called bombogénesis, which creates what is known as a bomb cyclone.
When talking about the storm, some climate forecasters have referred to a “bomb cyclone”. Calling it a “bomb” sounds fatal, but such storms are not exceedingly rare; recently there was one in New England.
What makes a storm a “bomb” is how fast the atmospheric pressure drops; the fall of atmospheric pressure is a characteristic of all storms. By definition, the barometric pressure must drop at least 24 millibars in 24 hours for a storm to be called a bomb cyclone; the formation of a storm like that is called bombogenesis.
Here’s how it works: Deep drops in barometric pressure occur when a region of warm air meets a region of cold air. The air begins to move, and the rotation of the earth creates a cyclonic effect. The direction is counterclockwise in the northern hemisphere (when viewed from above), leading to winds coming out of the northeast, a Nor’easter.
That was what happened at the end of October, when hot air from the remains of a tropical cyclone on the Atlantic collided with a cold front from the Midwest. Among other impacts, more than 80,000 electric customers in Maine lost energy because strong winds brought down trees.
A similar effect occurred on Wednesday, when warm air over the ocean met the extremely cold polar air that had descended over the east. The pressure was expected to fall rapidly from Florida to the north.