What is a bomb cyclone?

A severe winter storm — named Winter Storm Elliott by The Weather Channel — is projected to intensify into a so-called bomb cyclone as it dumps extreme winter precipitation across the Midwest heading into the weekend.

Bomb cyclones are hurricanes that form in winter through a process known as bombogenesis or explosive cyclogenesis, the meteorological term for when a midlatitude cyclone undergoes rapid intensification at speeds of at least 24 millibars, the measure of atmospheric pressure, over a 24-hour period. The phenomenon usually occurs in the winter months, but has occurred in the summer months on rarer occasions.

Conditions for this rapid intensification often result when a cold and warm air mass collide. The speed of intensification can cause temperatures to drop — in the case of Great Plains and upper Midwest states, temperatures have plunged in minutes as the mass of arctic air moves south.

“In this case, we are expecting it to deepen pretty rapidly there over the Great Lakes,” Alex Lamers, a warning coordination meteorologist with the National Weather Service, told The Hill.

While the blizzard conditions from the storm are likely to predominantly affect the Midwest, experts say bomb cyclones can lead to extreme weather at the fringes as well. In this case, the storm is projected to deliver rainy conditions up the East Coast, and forecasters have projected high winds and heavy rain in the northeastern U.S.

“Any time you get a rapidly deepening storm system like this, and it’s encased in a lot of cold air, you’re going to get really strong wind gusts over [a] very big area, which is what we’re seeing pretty much anywhere from the Rocky Mountains to the Atlantic coast,” Lamers said. “We’re expecting gusts of 40 miles an hour or stronger, and it will be stronger in some areas, particularly in the in the plains and then also the Northeast.”

“We may actually see gusts upwards of 60 miles an hour in those areas,” he added.

This week’s bomb cyclone is somewhat unusual, Lamers said, because conditions are usually better for bombogenesis along the coast, where arctic air is more likely to encounter warmer waters.

“To have one point quite so strong this far inland, where the deepening is really taking place over the Great Lakes, that is a little more unusual,” he said. “We don’t often see that.”