According to the National Ocean Service
Bombogenesis occurs when a midlatitude (the latitudes between the tropics and polar regions) cyclone rapidly intensifies, or strengthens, over a 24 hour period. This intensification is represented by a drop in millibars.
The American Meteorological Society defines a “bomb” as:
An extratropical surface cyclone with a central pressure that falls on the average at least 1 mb h-1 for 24 hours.
Simply put, this means a storm is intensifying very quickly
, which can result in more severe impacts, than what a weaker storm would produce. Most [but not all] Bomb Cyclones develope over water
, more often on the US East coast
, than the West.
The intensification required to classify as "bombogenesis" varies by latitude. At 60 degrees latitude*
, it is a drop of at least 24 millibars (24 hectopascals) over 24 hours. At the latitude of New York
City, the required pressure drop is about 17.8 millibars (17.8 hectopascals) over 24 hours.
Bombogenesis can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters. It is popularly referred to as a bomb cyclone.
To calculate the pressure drop needed for a bomb cyclone, you take the sine of the latitude where the low pressure is located, and divide it by the sine of 60 degrees*
. Multiply that result by 24, and that is the number of millibars the storm's pressure must drop, to officially qualify it as a bomb cyclone, at the given latitude.
Why 60 degrees? Swedish meteorology researcher, Tor Bergeron, initially defined "rapidly deepening" storms as those that met the 24 millibars-in-24 hours criterion, and that's the latitude where Bergeron was, when he developed the initial scale.