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The strong coastal storm that whipped up so much wind, knocking out power to nearly half a million electric customers in Massachusetts by Wednesday morning, underwent “bombogenesis,” according to forecasters. What’s that?

A storm undergoes bombogenesis — or, if you want to make it sound more ominous, “bombs out” — when its pressure drops steeply within a 24-hour period and it rapidly intensifies.

The technical definition of bombogenesis is when the atmospheric pressure drops at least 24 millibars over 24 hours.

“As expected this low pressure underwent bombogenesis. Using Nantucket as an example, the 3 AM pressure was 980 mb, while it was 1008 mb at this time yesterday morning. Other nearby surface observations show similar conditions,” National Weather Service forecasters said Wednesday morning in an Internet posting. That was a 28-millibar drop.

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“In the last 2-3 hours,” forecasters wrote at 7 a.m., “there was a narrow swath of 60-80 mph gust that impacted southeastern MA and RI, which coincided with the bombogenesis and associated spike in power outages to over 400k customers in MA.”

A large tree fell onto a pickup truck in Fairhaven, Mass. on Wednesday, Oct. 27, 2021 as a nor'easter slams into the region. (Peter Pereira/The Standard-Times via AP)
A large tree fell onto a pickup truck in Fairhaven, Mass. on Wednesday, Oct. 27, 2021 as a nor'easter slams into the region. (Peter Pereira/The Standard-Times via AP)PETER PEREIRA/The Standard-Times/Associated Press

The term bombogenesis — which can also be referred to even more ominously as “explosive cyclogenesis” — was coined by the late meteorology professor Frederick Sanders. Sanders, who died in 2006, is credited with using the word “bomb” to describe explosively intensifying winter storms, MIT says. The term became familiar to many in Massachusetts during winter storms in recent years.

“During winter, such cyclone bombs can cause intense cyclones just off the east coast of the USA with storm-force winds, high waves, and blizzards or freezing rain,” according to the textbook “Practical Meteorology” by Roland Stull.

Material from prior Globe stories was used in this report.

Read more:

- This was one powerful storm, and its impact will be felt for days to come

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- Nor’easter topples trees, downs power lines, and causes ‘impassable’ roads




Martin Finucane can be reached at martin.finucane@globe.com.