You may have heard the term “Bomb Cyclone” recently. We’ve been using it a ton this past week, in reference to the powerful storm system that impacted the West Coast to yield record-breaking rainfall, hurricane-force winds, and interstate-blocking landslides. That said, the bomb’s copious rainfall also produced some positive effects— it put a final end to the devastating months-long Dixie Fire in northern California, and resurrected one of the state’s most iconic natural features, Yosemite Falls. 

But what does the term “Bomb Cyclone” actually mean, sounds almost made up, right? Well, believe it or not, just like Polar Vortex, it is a real meteorological term. A “Bomb Cyclone” is a type of mid-latitude cyclone aka our most common weather-making system. Meteorologists decipher the strength of all cyclones (including hurricanes) by their lowest central pressure which is measured in millibars. 

A bomb forms when a mid-latitude cyclone undergoes bombogenesis (man, we have some cool words in weather). Bombogenesis is defined by a drop in central pressure of 24 millibars or more in the span of 24 hours. This indicates that the storm system has rapidly and explosively intensified.

The most common time of the year for bombogenesis to occur is from October to March and is not confined to the West Coast, in fact many Nor’easters are the product of bombs. 

The term was first coined in 1980 by famed Swedish meteorologist Tor Bergeron who is best known as the father of cloud physics.