What is a bomb cyclone? A winter hurricane, explained.
- Bombogenesis is said to occur when a storm's central barometric pressure drops at least 24 millibars in 24 hours.
- In the 1940s, some meteorologists began informally calling some big coastal storms "bombs."
- Many nor'easters – big storms that wallop the East Coast – are the product of bomb cyclones.
Sometimes in the winter, you'll hear weather folks describing a big storm as a bomb cyclone. But what, exactly, is it?
A bomb cyclone, which occurs through the process known as bombogenesis, is basically a winter hurricane.
A bomb cyclone "occurs when a mid-latitude cyclone rapidly intensifies," or quickly drops in atmospheric pressure, marking the strengthening of the storm, according to the National Oceanic and Atmospheric Administration,
Bombogenesis is said to occur when a storm's central barometric pressure drops at least 24 millibars in 24 hours. A millibar is a way of measuring pressure. The lower the pressure, the more powerful the storm.
Some storms have intensified as rapidly as 60 millibars in 24 hours. A few bomb cyclones even develop "eyes," similar to the center of a hurricane.
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In fact, a bomb cyclone can rival, in some aspects, the intensity of strong hurricanes in the Atlantic. For example, a bomb cyclone could be at the intensity level of Hurricane Larry, a long-lived and intense cyclone that churned across the Atlantic in early September 2021, according to AccuWeather.
The word "bombogenesis" is a combination of cyclogenesis, which describes the formation of a cyclone or storm, and bomb, which is, well, pretty self-explanatory.
"This can happen when a cold air mass collides with a warm air mass, such as air over warm ocean waters," NOAA said. "The formation of this rapidly strengthening weather system is a process called bombogenesis, which creates what is known as a bomb cyclone."
In the 1940s, some meteorologists began informally calling some big coastal storms "bombs" because they develop "with a ferocity we rarely, if ever, see over land," said Fred Sanders, a retired MIT professor who brought the term into common usage by describing such storms in an article in the journal Monthly Weather Review in 1980.
Even though bomb cyclones sometimes share characteristics with hurricanes, it is important to note that they are not hurricanes, and the two kinds of storms are different in important ways:
Bomb cyclones have cold air and fronts
Cold air rapidly weakens hurricanes, while it is an essential ingredient for bomb cyclones.
Bomb cyclones form during winter
Hurricanes form from late spring to early fall, while bomb cyclones form from late fall to early spring.
Bomb cyclones form at higher latitudes
Hurricanes form in tropical waters, while bomb cyclones form over the northwestern Atlantic, northwestern Pacific and sometimes the Mediterranean Sea.
Many of the infamous storms that have battered the East Coast and sank ships in the northwestern Atlantic Ocean throughout history were bomb cyclones.
And many nor'easters – big storms that wallop the East Coast – are the product of bomb cyclones, according to meteorologist Jeff Haby of the WeatherPrediction.com.
How bomb cyclones form
First stage: A stationary front of dry cold air and moist warm air forms.
Second stage: The two fronts move against one another.
Third stage: The fronts begin to rotate around a low-pressure center.
Fourth stage: The cold air displaces the warm air, forcing it to rise. That fuels a change in temperature, which causes the air pressure to drop.
If the decrease in air temperature is severe enough — 24 millibars in 24 hours — bombogenesis takes place and a bomb cyclone results.
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Contributing: George Petras/USA TODAY