What sparked the 'bomb cyclone'? Huge temperature contrasts, jet stream energy

It all started innocently enough.

Shortly before New Year's celebrations kicked off in the Southeast, a record-cold air mass blew in from the north. This air had a direct connection to the Arctic, spilling out as if someone left the Northern Hemisphere's refrigerator door open.

This frigid air oozed across the Gulf of Mexico, into Florida, and served as one of the catalysts for a low pressure area to develop in the Bahamas on Tuesday. Snow flurries were even reported on an oil platform off the coast of Louisiana.

The cold air sitting over unusually warm Atlantic Ocean waters helped set up a huge thermal, or heat, contrast, which the East Coast's bomb cyclone was then able to take advantage of and intensify at nearly unheard of rates late Wednesday and Thursday.

During the 24 hour period ending at 10 a.m. ET on Thursday morning, the storm's central air pressure dropped by 59 millibars, to 951 millibars, which put the blizzard in the upper echelon of rapidly intensifying storms. No other non-tropical storm has intensified this rapidly off the Mid-Atlantic and Northeast coast in the past 30 years or more.

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After the cold air moved into the Southeast, all that was needed for a storm to form was a trigger to come along. Mother Nature delivered multiple triggers on Wednesday, when three distinct, potent waves of energy embedded within the jet stream moved over the area.

According to meteorologist Alex Lamers of the National Weather Service's Weather Prediction Center in College Park, Maryland, meteorologists are scrambling to understand how this storm got so strong, so quickly.

The temperature contrast was just one of the key ingredients that set this storm off, he said. “You had a really anomalously cold air mass south to the Gulf," Lamers said in an interview. “I think that was a big driver, just the big gradients in temperature and moisture,” he said.

Some other factors, he said, may not be known now, and will require further study by researchers.

“I think that was probably a big factor, and then jet [stream] dynamics probably played a big role too,” Lamers said.

Winds at the upper levels of the atmosphere, within the highway of air that steers weather systems, promoted ascending air and storm intensification, Lamers said.

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Sam Lillo, a meteorology Phd. student at the University of Oklahoma, said the jet stream disturbances acted "like a vacuum, evacuating mass out of the column of atmosphere [and] resulting in decreasing pressure at the surface."

"Even one shortwave interacting with the low and its subtropical connection would've resulted in a strong Atlantic storm. The three shortwaves also aren't perfectly phasing, so the actual ceiling for the strength of this storm was likely even higher."

Another ingredient in the bomb cyclone was unusually warm sea surface temperatures in the Western Atlantic, Lillo said in a Twitter message. "These origins, along with the unusually high Atlantic sea surface temperatures are important because there has been extraordinary influence from latent heat fluxes and deep convection in this storm...," he said, referring to the formation of powerful thunderstorms as part of the low pressure area.

The above normal sea surface temperatures also produced an unusually sharp zone of temperature contrasts, which helped to fuel the low pressure area, Lamers said. Such storms, after all, feed off of the differences in air masses, so the bigger the contrast in air masses, the stronger the storm may get.

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In the end, meteorologists may have a much greater interest in a storm's intensification rate than everyday people.

The main difference between a rapidly intensifying storm like the one on Thursday and one that intensifies at a more typical rate for the Northeast is that storms that undergo bombogenesis tend to produce higher wind gusts, as well as more thunderstorms. They can also be more difficult to predict, since computer models may struggle to predict their complex evolution.

With winds gusting to at least 80 miles per hour, and a foot-plus of snow already falling in the Mid-Atlantic and New England, it's clear that the bomb cyclone of 2018 lived up to most of the hype. Now it's up to meteorologists to figure out how to better predict more storms like it in the future.