Thanks to the warping of the jet stream that crosses the Arctic, much of the United States is currently in the grip of an overly harsh and record-breaking cold snap. Sharks have reportedly washed up on beaches frozen to death, parts of the Niagara Falls have turned into crystalline marvels, and the President of the United States is talking out of his posterior with regards to climate change science.
As first reported by the Capital Weather Gang over at the Washington Post, the deep chill isn’t over yet. A rather peculiar meteorological phenomenon named a “bomb cyclone” is about to hit the East Coast this week which they said, not necessarily unfairly, will “resemble a winter hurricane.”
It will begin with a storm whipping the coastal parts of southeastern US, bringing with it blizzard-like conditions. Florida, for example, is already getting a fair bit of rain, sleet and snow dumped on it.
The system is predicted to then move out into the Atlantic Ocean near to New England, and models suggest that it will have hurricane-strength winds by around Thursday. Biting cold and plenty of snow will fall across parts of the US for a day or more.
So, at this point, we hear you asking: What the heck is a bomb cyclone, or even a winter hurricane? Well, rather bemusingly, there appears to be some disagreement as to what this phenomenon actually is.
According to plenty of meteorologists, a bomb cyclone is a real term. The system’s sudden drop in pressure appears to be where the “bomb” term has emerged from. The UK Met Office explains that a “weather bomb” is a somewhat unofficial term for a low-pressure system – like a storm or hurricane – whose core pressure drops by 24 millibars in 24 hours. In the US, this is sometimes known as bombogenesis.
“Meteorologically speaking, the process is known as explosive cyclogenesis. In this instance, the pressure system within 12 hours will drop from 995 millibars to 952 millibars,” Oli Claydon, a spokesperson for the UK Met Office, told IFLScience.
As pointed out by meteorologist James Kossin over at The Daily Beast, however, this isn’t a “winter hurricane”. Although the storm will probably bring hurricane-force winds, it’s not technically a hurricane. It's just a storm.
“Hurricanes need a set of specific variables at play, which they are not at the moment,” Claydon adds.
First, a quick recap. Hurricanes – defined by their rotating structure, their low internal pressure and (primarily) their wind speed – are geographical variants of tropical cyclones, which is the generic name for them. As the name suggests, they form over the tropics, build up strength over warm, summer oceanic waters, and miss or slam into parts of the Americas.
Hurricanes Harvey and Maria, for example, were tropical cyclones. This latest storm, however, does not share their characteristics. Not only is it forming at a strange time of year – in the frigid winter – but it's also appearing at an unusually high latitude.
According to meteorologist Ryan Maue, and the Weather Channel’s meteorologist Greg Postel, it’s likely to become, or already is, an extratropical cyclone, a cyclonic storm system with a lower cold core that forms outside of the tropics.
Remember, though, that just because it's cyclonic, it doesn't mean it's a hurricane; it is just a pretty potent storm. Claydon tells us that "you can describe storms as zones of cyclonic low pressure. It's just talking about the way the wind is flowing.”
Yes, December/January cyclones in this part of the world do sometimes occur, but genuine hurricanes are extremely uncommon, and they require unseasonably warm ocean waters or extremely chilly atmospheric temperatures – or both. In this particular situation, various atmospheric wedges have conspired to generate an unexpectedly energetic storm system.
Mashable hints that the temperature gradient required to generate an extremely powerful extratropical cyclone is present right now in the region, but again, it’s unclear as to what this storm will ultimately become by Thursday. In any case, at this stage, then, we can definitely call it a bomb cyclone.
At the very least, it's a phenomenon that will dump a heck of a lot of snow in places that don't normally experience it, which sounds like the result of a wizard casting a particularly powerful spell, or even the emergence of a potentially zombified ice dragon.
Update: Meteorologist Eric Holthaus of Grist has since pointed out that the bomb cyclone is the most rapidly deepening winter storm in this part of the world since at least 1980, and perhaps earlier.