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Atlantic Canada Nor'easter: Bomb cyclogenesis

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By Gina Ressler
Wednesday, March 26, 2014, 11:53 AM

Over the past week, our meteorology team has been busy nailing down the forecast details for what will likely be the strongest storm for Atlantic Canada this year.

TUNE IN FOR LIVE COVERAGE: Chris St. Clair will on location in PEI, Chief Meteorologist Chris Scott and Meteorologist Mark Robinson will be monitoring the storm from Cape Breton and Nathan Coleman will be on location in Halifax.

Confidence is growing that this will be a powerful Nor'easter, undergoing what meteorologists call “bomb cyclogenesis”, or rapid intensification. East coasters are used to a handful of Nor'easters each winter, but this one will be a powerhouse. Some forecasters are already drawing comparisons between this week's storm and White Juan, the powerful Nor’easter that buried Atlantic Canada in snow 10 years ago.

What is “bomb cyclogenesis”? 

Like this winter’s ubiquitous “polar vortex”, “bomb cyclogenesis” (or “bombogenesis”) is a real meteorological term that has made its way into the public lexicon thanks to some recent high impact storms and the power of social media.

The term “bomb cyclone” was coined around 1980 by Fred Sanders, one of the grandfathers of synoptic meteorology, and his student, John Gyakum, now a professor at McGill University.

ATLANTIC CANADA NOR'EASTER: Eight weather terms you'll be hearing this week

The most common definition of a “bomb” is an extratropical cyclone whose central pressure falls 24 millibars in 24 hours -- i.e. very rapid deepening. And if we’re getting technical, it should be noted that the criteria for bomb cyclogenesis varies by latitude, from 28 mb / 24 hr at the pole to 12 mb / 24 hr in the subtropics.

This week’s storm could deepen by as much as 40 to 50 millibars in 24 hours, depending on which model you choose. By Wednesday afternoon, our Nor’easter could have a central pressure as low as 950 mb as it swing north towards Cape Breton.

This run of the CMC-RDPS model shows a 48 millibar drop in 24 hours. Courtesy: meteocentre.com

This run of the CMC-RDPS model shows a 48 millibar drop in 24 hours. Courtesy: meteocentre.com

While Nor’easters themselves are common in the depths of winter, the strength of this week’s storm is incredible for late March. It’s tough to say exactly how rare this week’s storm is, since historical records aren’t complete. A search through reanalysis data provides some insight. Storms will a central pressure less than 968 mb are far more common in January or February than in March or April.

Data from NCEP Climate Forecast System Reanalysis (CFSR). Courtesy: Shawn Milrad

Data from NCEP Climate Forecast System Reanalysis (CFSR). Courtesy: Shawn Milrad

Based on initial research, a spring Nor’easter of this strength only occurs roughly once every decade or so.

Ingredients of a Nor’easter Bomb

Although strong Nor’easter bombs can generate winds speeds near hurricane strength, they derive their energy from a different source: the clash between warm and cold air.


Atlantic Canada storm: Environment Canada calling for zero visibility, wind gusts up to 180 km/h
This Nor’easter versus White Juan
Atlantic Canada Nor'easter: Eight weather terms you'll be hearing
Nor'easter coverage: Nine maps that explain everything

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