If you live in the eastern US, from northern Florida all the way to New England, you’re in for some nasty weather: a massive winter storm called a “bomb cyclone” is hammering the coast, bringing snow, ice, flooding, and strong winds. That’s not a made-up click-bait term; it’s actually used by meteorologists to indicate a mid-latitude cyclone that intensifies rapidly — or as meteorologist Jon Martin at the University of Wisconsin-Madison says, they “just kind of explode.”
“We would think of them as explosive events, they just instantly appear and get very strong,” he says. This particular bomb cyclone could become one of the most intense off the East Coast in decades, according to The Washington Post.
A bomb cyclone happens when atmospheric pressure in the middle of the storm drops at least 24 millibars over 24 hours, quickly increasing in intensity. (The lower the pressure, the stronger the storm.) This particular bomb cyclone sweeping through the East Coast is forecasted to drop by 36 millibars, which is a lot. According to Martin, it means the storm is going to lose the equivalent of about 3.5 percent of the entire mass of the whole atmosphere, from the ground to outer space. “It’s exceptionally intense,” he says. “That’s the most unusual thing about this storm.” (Unlike hurricanes or tropical cyclones, winter storms don’t get named by the National Weather Service. Sorry, storm. But some news outlets and The Weather Channel are referring to it as Winter Storm Grayson.)
This sort of winter hurricane formed because of the serendipitous convergence of several factors, including a blast of freezing air from the North Pole that, right off the southeast coast of the US, has come into contact with warm ocean waters carried by the Gulf Stream. That strong temperature contrast is what sparks and intensifies the storm so rapidly, says Andrea Lang, assistant professor of atmospheric and environmental sciences at University at Albany.
The other unusual thing about this winter storm is it’s farther south than normal, according to Bob Oravec, lead forecaster with the National Weather Service. Typically, you don’t see winter storm warnings in states like Georgia and South Carolina, Oravec says.
Why this is happening is complicated, but Martin says it can be attributed to how the air flows in the atmosphere. This year, we’ve had a giant ridge of high pressure sitting over the West Coast, which has brought warm air up all the way to Alaska and is in part to blame for the massive wildfires that have plagued California. The ridge also has consequences on the other side of the country. “If you wiggle the jet stream at one end, there’s going to be a wave that propagates along it,” Lang says. That wave has dragged freezing Arctic air down south into the eastern US, where then it got into contact with the warm ocean waters — sparking the bomb cyclone.
As hellish as the storm may seem to the poor souls on the East Coast, it’s not unprecedented. “It doesn't happen every day, but it's not unheard of,” says Oravec. “History is full of huge snow storms along the East Coast and history will continue to be full of huge snow storms along the East Coast going forward.” Still, it’s going to bring hazardous, blizzard conditions that people should take seriously. There might be power outages, and traveling could be dangerous.
The storm is moving very quickly, so it won’t lead to record snow, Oravec says. Most of the snow will happen along the coast today and tomorrow, and then very cold winds will hammer the northeast US, possibly bringing record-shattering freezing temperatures on Friday and over the weekend. After that, we can expect a break from the big chill — but that won’t last long.
By Tuesday and Wednesday, more Arctic air is going to sweep through the US all the way to the East Coast again — just the sort of “welcome back” from the holidays we’ve all been waiting for.
Update January 4th, 9:19AM ET: The story has been updated to clarify that winter storms aren’t named by the National Weather Service, but can be named by others. “Anyone can name it anything that they want,” Oravec says.