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A massive winter storm battered the eastern United States (US) on Christmas Day, Sunday, 25 December, with frigid temperatures, high winds, and heavy snow leaving at least 31 people dead.
A crisis unfolded in Buffalo, New York, where the storm prevented emergency services from reaching high impact areas.
Over 200,000 people across the eastern US woke up without electricity on Christmas morning, and many more had to cancel their holiday plans, even though the storm, which has been wreaking havoc in the region for the last five days, showed some signs of easing.
Travelers were stranded at several airports on 25 December, including in New York, Atlanta, Chicago, Detroit, and Denver.
Meteorologists are calling the weather phenomenon a 'bomb cyclone.' But what exactly is a 'bomb cyclone'? Which states are being affected by it? The Quint answers these questions for you.
What is a Bomb Cyclone?
According to The Washington Post, the clearest definition of a 'bomb cyclone' is that it is a mid-latitude storm whose central air pressure dips at the rate of one millibar per hour for at least 24 hours.
To put it into perspective, normal air pressure is about 1,010 millibars, a measurement of the force exerted by the weight of the atmosphere.
But what happens during stormy weather is that the air pressure drops well below that. In fact, the lower the pressure, the stronger the storm.
The pressure of the storm system sweeping across the US is forecast to fall from 1,003 millibars to 968 millibars. This is a drop of 35 millibars and is more than enough to qualify as what meteorologists call "explosive bombogenesis" – a rapid intensification.
How Do Bomb Cyclones Form?
Like any other storm, a bomb cyclone develops when drastically different air masses collide – typically, cold and dry air moving down from the north, and warm, moist air coming up from the tropics.
The warmer air swiftly rises, creating cloud systems, lowering air pressure, and developing into a storm system that circulates counterclockwise around that centre of low pressure.
A rapid strengthening of the storm is an indicator that increasing amounts of warm air are being drawn into a storm's circulation, spiraling toward its centre and rising out its top.
When more air escapes out the top of the storm than is being sucked inward, the air pressure dips even further.
The differences in air temperature that feed this process can be especially pronounced when a polar air mass is as cold as the one surging into the US currently. For instance on Friday, 23 December, the temperature dipped to -45°C in Montana.
How Do Bomb Cyclones Differ From Hurricanes?
As Daniel Swain, a climate scientist at the University of California, told Sky News, all bomb cyclones are not hurricanes.
He explained that bomb cyclones can take on characteristics that make them look a lot like hurricanes, with very strong winds, heavy precipitation, and well-defined eye-like features in the middle.
Hurricanes, typically, tend to form in tropical areas and are powered by warm seas. This is why hurricanes are common in the US in the summer or early autumn, when seawater is the warmest.
In contrast, bomb cyclones do not need balmy ocean waters to form, he elaborated.
They can appear over land as well as the sea and are most common between late autumn and early spring, when warm tropical air bumps up against frigid Arctic air.
How Strong Are Bomb Cyclones?
Bomb cyclones typically tend to produce heavy rain or snow, coastal flooding and hurricane-force wind gusts.
Swain said that fundamentally, the impacts of a bomb cyclone are not necessarily different from other strong storm systems "except that the fast strengthening is usually a signature of a very powerful storm system."
He added that much of the danger lies in the fact that bomb cyclones can take people by surprise.
One bomb cyclone that struck New England this year dumped as much as 2 feet of snow. Another that hit the Pacific Northwest in 2019 produced a 106-mph wind gust.
Why Is It Called a Bomb Cyclone?
The term was coined in a 1980 research paper by MIT meteorologists Frederick Sanders and John R Gyakum. Gyakum told The Washington Post that it was born out of a need to better communicate the intensity of storms outside summertime and hurricane season.
How Has It Affected Normal Life?
Thousands of people were faced with flight delays and cancellations on Friday, 23 December, as the winter storm blasted through the country.
About 10,400 flights within, into, or out of the US were delayed and an additional 5,753 were canceled, according to flight tracking website flightaware.com.
Near whiteout conditions were reported in Minnesota, Iowa, Wisconsin, and Michigan, while flash flooding inundated communities across several northeast states.
Tens of millions of people were under winter storm advisories or warnings, with meteorologists saying it was so cold that anyone venturing outside risked frostbite within minutes.
The National Weather Service (NWS) said temperatures of -45 degrees Celsius and -56 degrees Celsius were possible by the end of this week in some parts of US.
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