Published: March 14,2017
Winter Storm Stella has officially met "bombogenesis" criterion – an ominous-sounding term frequently used in the winter to describe powerful low-pressure systems that intensify rapidly.
To be classified as a weather bomb, or having undergone bombogenesis or "bombing out," the central pressure of a low-pressure system must drop at least 24 millibars within 24 hours.
At 8 p.m. EDT Monday, the central pressure was 1007 millibars, and as of 3:30 p.m. EDT Tuesday the pressure had dropped to around 976 millibars. This equates to a pressure drop of 31 millibars in only 19.5 hours, easily exceeding the requirements for bombogenesis.
The process of bombogenesis begins as cyclogenesis, or the development or strengthening of an area of low pressure or trough.
(MORE: 5 Things to Know About Winter Storm Stella)
Winter Storm Stella officially met bombogenesis criterion.Bombogenesis results when there is a large temperature gradient, usually between a cold continental air mass and warm sea-surface temperatures. It can also be the product of a cold polar air mass and much warmer air from the south, say, over the Plains states.
Over that temperature contrast, a powerful, intensifying jet stream disturbance triggers air to rise and begins the process. This happens most often from October through March, but is possible any time of year.
Frequently, nor'easters are weather bombs due to cold air surging southward from Canada, combined with the warm ocean waters from the Gulf Stream.
When a weather bomb strengthens, winds increase dramatically, and precipitation – including snowfall – can become intense. Blizzard conditions can occur, sometimes accompanied by lightning as the system is "bombing out."
(MORE: Difference Between 'Blowing' and 'Drifting' Snow and Their Hazards)
A Few Notable ExamplesIn February 2016, Winter Storm Mars underwent bombogenesis. The central pressure of this low-pressure system dropped from 1004 millibars at 7 a.m. EST on Feb. 7 to 979 millibars by 1 a.m. EST Feb. 8, or 25 millibars in only 18 hours. Blizzard conditions were verified in multiple locations on Cape Cod and a wind gust of 65 mph was measured on Nantucket Island.
An example of bombogenesis off the East Coast.In 2015, Winter Storm Iola exhibited bombogenesis when the pressure dropped from 1009 millibars to 980 millibars from 7 p.m. Jan. 23 through 4 p.m. Jan. 24 – a drop of 29 millibars in 21 hours. Strong winds from Iola caused coastal flooding to some locations in Massachusetts.
This also happened in February 2013, when Winter Storm Nemo dropped 29 millibars within a span of 24 hours (specifically, a barometric pressure of 1000 millibars was recorded at 4 a.m. on Feb. 8, and dropped to 971 millibars at 4 a.m. on Feb. 9). Winter Storm Nemo ultimately "bottomed out" with a minimum barometric pressure reading of 968 millibars at 4 p.m. on Feb. 9. This powerful low-pressure system resulted in a wind gust of 83 mph near Cuttyhunk, Massachusetts, and thundersnow was reported on Long Island.
(MORE: 8 Cool Things to Look for During Winter)
Mars, Iola and Nemo all brought snow to areas of the Northeast, but although weather bombs typically are found during the winter with a marine influence, this is not always the case.
An example of bombogenesis over land was the "Octobomb" that impacted portions of the Plains and Midwest Oct. 25-27, 2010. All-time record low barometric pressure readings in Minnesota and Wisconsin were set by this system.
Tropical cyclones can also undergo rapid intensification, which is a particularly unnerving development, especially when it occurs near landfall. An example of a tropical cyclone undergoing bombogenesis is Hurricane Charley in 2004.
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