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The bomb cyclone isn't a winter hurricane — just a bad storm with good branding

A meteorologist explains the storm about to hit the East Coast.

Weather feature - Washington, DC Matt McClain/Washington Post via Getty Images
Jen Kirby is a senior foreign and national security reporter at Vox, where she covers global instability.

A huge swath of the United States is trapped in a deep freeze — and even more extreme weather is on the way. The East Coast is bracing for a “bomb cyclone,” a winter weather storm that will torment a region from Florida to Maine with sleet, snow, and winds.

This “bomb cyclone” is defined by a very specific and very extreme drop in atmospheric pressure — 24 millibars in 24 hours. That means the storm will pack a powerful punch, with winds that could whip at hurricane-force strength.

The bomb cyclone will wallop the Eastern Seaboard Wednesday into Thursday. But even more bone-numbing Arctic cold will follow in its wake. Cold temperature records will likely be shattered, as highs in the mid-Atlantic states and New England will be in the teens and single digits Friday into Saturday.

I spoke to Ed Vallee, a North Carolina meteorologist, to understand this one-two punch of bomb cyclone and brutal chill. “A lot of people,” he warned, “are going to be very cold.”

This interview has been edited and condensed for clarity.

Jen Kirby

So is “bomb cyclone” a real term?

Ed Vallee

It is definitely a real term, and there’s a strict definition that has to happen for it to be considered a “bomb.” The strength of an area of low pressure — so a storm system — is measured in what we call millibars. The lower the millibars, the stronger the storm. The official definition of a “bomb” is for an area of low pressure to strengthen at least 24 millibars in 24 hours.

Jen Kirby

That sounds like an intense phenomenon. What conditions have to be present to make that bomb happen?

Ed Vallee

Atmospheric dynamics are going to differ by storm, but in this situation, there is a really tight temperature gradient along the East Coast. You have the Gulf Stream just off the Southeast Coast there, and you have all this really cold air coming in from the North. When you have this really tight temperature gradient, you can get these pieces of energy — weather disturbances — coming through the atmosphere. When they phase together with that really tight temperature gradient, that’s the ingredient you need to have a storm start to strengthen really rapidly.

The bomb is really not that uncommon, but it does indicate a very strong, strengthening low-pressure system. Under the right conditions, that can lead to a very strong storm and ultimately some pretty good snowfall across the Northeastern US.

Jen Kirby

What do you mean when you say “tight temperature gradient”?

Ed Vallee

When you have the Gulf Stream just off the East Coast, that naturally leads to warmer conditions, and when you get this cold air coming in behind it — or coming in from the North — that leads to that very tight temperature gradient from just off the Southeast Coast onto the mainland of the East Coast. Those types of temperature gradients are typically a railroad track, so to speak, that the storms can form along and ride up along, and that kind of helps to increase the lift in the atmosphere and ultimately the amount of precipitation that falls.

Jen Kirby

Is there something specific about the storm that is unique in its formation or impact?

Ed Vallee

The dynamics between this storm and, say, a typical Nor’easter really aren’t that different — it’s just that this is one a) is going to be the first one of the year, and b) it’s a more wide-ranging storm, from Florida all the way up to Maine.

Jen Kirby

I’ve seen some outlets compare this to a “winter hurricane,” though some meteorologists have pushed back on that language. Why is that the wrong comparison to make?

Ed Valle

They’re two totally different systems. Hurricanes feed off warm water and are totally different dynamically compared to a winter storm. Storms that are of hurricane strength, or have hurricane-strength winds, happen all the time. They happen every winter. This isn’t a crazy anomaly in any way, shape, or form.

Jen Kirby

So winter storm, just really strong winds.

Ed Vallee

People are taking the pressure reading in the storm, and then they’re instantly comparing it to a hurricane, which is not true because the dynamic factors are totally different.

Jen Kirby

So, dumb question. Why is it called a cyclone then?

Ed Vallee

All cyclones move the same way in the Northern Hemisphere. They’re all low-pressure systems, but the way they develop and how they interact with the atmosphere around them are completely different.

Jen Kirby

Even though it’s not a hurricane, when we talk hurricane-force winds, how strong will those typically be?

Ed Valle

Typically, over land, with these types of systems there could be hurricane-force wind gusts that could be 74 mph or greater along the southeastern New England coast. But to be honest with you, I think most of the winds are going to stay below that. I think it’s more along the lines of 35 to 55 mph gusts. Over the Atlantic, where there’s no land interaction with the wind, and closer to the storm’s center, those areas definitely can see winds in excess of 74 mph, which is technically the criteria to meet for hurricane-force wind.

Jen Kirby

What’s the general forecast up and down the East Coast? It seems the winds, more than snow, are going to be the biggest deal.

Ed Vallee

It’s all relative — that’s another really important factor to keep in mind. Northern Florida, if you’re going to get even just a little bit of snow, that’s different than obviously up in New York. But it is going to be a wide-reaching area of wintry precipitation from the Panhandle of Florida all the way up to the coastal Carolinas. They’re going to see a few inches of snow and some ice as well, and then once the storm system gets to just about the latitude north of Virginia or so, that’s when the heavier snowfall threat is really going to start occurring, as the system starts to gather strength and “bomb out.”

Once we get toward the southern Delmarva up into coastal New Jersey, central and eastern Long Island, and then eastern New England — that’s where the snow is really going to be the bigger impact. But for the South, while it might not be a lot of wintry precipitation, pretty much any wintry precipitation down here [makes] people freak out.

Jen Kirby

It’s been freezing here on the East Coast. I understand it’s going to be even more freezing after this storm comes through. Why is that going to happen?

Ed Vallee

You get a lot of cold air coming in behind the system, and because the system is going to be so strong, it’s going push down even more colder air leading to even more — frankly brutal — winter conditions into late Thursday through the weekend.

Jen Kirby

This bomb and cold weather system is really going to stretch up and down the East Coast from Northern Florida all the way to New England?

Ed Vallee

That’s exactly right. It’s going to form in the Southeast and move up the coast. That cold air is going to wrap in all the way down into the Panhandle of Florida and Northern Florida. It’s a very wide-reaching cold outbreak, more so than the precipitation just because of the aerial coverage. A lot of people are going to be very cold.

Jen Kirby

So the “bomb cyclone” followed by the “polar vortex,” essentially.

Ed Vallee

There are your buzzwords, that’s right.

Jen Kirby

What’s with this ridiculous cold spell, anyway? The East Coast has been so cold for so long.

Ed Vallee

Simply put, the pattern in the upper level atmospheric in the Pacific Ocean has been favorable [for] some of these cold shots to come right down into the United States, and that’s something we haven’t really seen in December. It’s definitely a difference compared to past winters because we just haven’t seen that type of cold. This regime is the coldest we’ve been nationally since 2013 to 2014, and we’re in a very similar type situation where the pattern is such that it drove the cold right down into the Central and Eastern United States.

You can also, if you want to throw a couple of buzzwords — we have been impacted by the tropospheric polar vortex. Or you can just say polar vortex — we are being impacted by part of that polar vortex, which is enhancing the overall cold regime.

Jen Kirby

Is there anything particular about this upcoming bomb cyclone and the cold spell following it that I might have missed?

Ed Vallee

The big thing in New England, and then down in the Carolinas in the Southeast, where snow is not really common, the snow and ice are going to be the bigger concerns. New England [could get] heavier snow — but for a lot of the big population centers like Washington, DC, Baltimore, even Philly, maybe the western suburbs in New York City, there’s going to be some snow, but not enough for people to be like, “The storm is incredible.”

That area — that’s where the cold and the winds are going to be the biggest concerns. The cold and the wind that could lead to some power outages, so with this extreme cold that’s coming, people just need to make sure they’re prepared for whatever they need to do to stay warm.

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