By Jeremy Deaton -
NBC News
A powerful winter storm is expected to hit millions of people across much of the United States beginning Wednesday, bringing freezing temperatures, heavy snow and life-threatening wind chills.
Extreme weather will complicate Christmas travel for
some 200 million Americans across a wide swath of the country
, from the Central Plains and Midwest to the Atlantic coast.
But it can also lead to the formation of what forecasters call a "cyclone bomb," which would push temperatures to record lows on the Gulf Coast and northeastern United States as early as Friday.
We explain what this climatic phenomenon is about and why it is so dangerous.
What is a bomb cyclone?
A bomb cyclone is a rapidly intensifying storm that forms when air near the Earth's surface rises rapidly into the atmosphere, causing a sudden drop in barometric pressure—at least 24 millibars in 24 hours.
As the air rises, the wind spirals into the base of the storm.
As it rises to the top at a faster rate than it can be replaced at the bottom, the barometric pressure continues to drop.
As with hurricanes, lower atmospheric pressure produces a more intense storm.
[USA. prepares for one of the coldest Christmases and effects on airports and highways]
“Not all bomb cyclones are hurricanes
,” explains Daniel Swain, a climatologist at the University of California, Los Angeles.
"But sometimes they can take on characteristics that make them look a lot like hurricanes, with very strong winds, heavy rainfall, and well-defined eye-shaped features in the center."
Why is it called a bomb cyclone?
Meteorologists have compared the sudden drop in barometric pressure in this phenomenon to the explosion of a bomb, using words like "explosive cyclogenesis" and "bombogenesis" to describe the process of storm formation.
A woman clears snow in New York in a November 2022 photo. John Normile / Getty Images
Although it may not seem like it, “bomb cyclone” is a legitimate scientific term.
"You can find it in the American Meteorological Society Glossary," Swain said, adding that
the term refers specifically to the speed with which the storm forms and
"not necessarily its strength."
How is it different from a hurricane?
Hurricanes usually form in tropical areas and are fed by warm waters, so they are more common in the summer or early fall when the sea water is warmer.
Bomb cyclones, on the other hand,
do not need warm ocean water to form
.
Although they sometimes appear there, they can also appear on land, as happened with the cyclone that hit the northern plains in March 2019.
[Authorities ask to take precautions due to low temperatures during the Christmas season]
Unlike hurricanes, bomb cyclones arise in mid-latitudes, where sources of warm and cold air collide.
They rarely appear in the summer, when the weather is warm in the Northern Hemisphere, and form between late fall and early spring, when tropical air collides with frigid arctic air.
“They tend to appear at the time of year when there is a chance that warm and cold air will occur at the same time,” Swain said.
It is the difference in temperature that fuels the drop in pressure.
Are bomb cyclones dangerous?
It depends, sometimes they behave like regular winter storms, but at other times they
cause
intense flooding, snowstorms
and wind
speeds similar to those of a Category 1 hurricane.
They report more than 1,500 delayed flights and at least 200 canceled due to bad weather
Dec 21, 202200:42
“The impact of a bomb cyclone is no different than any other strong storm system, except that rapid strengthening is often the signature of a very powerful storm system,” said Swain, noting that
much of the danger is that bomb cyclones take people by surprise
.
To stay safe during these types of events or if another severe storm approaches, experts recommend
storing canned food, water, medicine
and first aid supplies, flashlights, and batteries.
They also suggest checking that your vehicle has a full tank of gas and is ready to go, if necessary.
Homeowners should be prepared with salt and snow shovels to clear sidewalks and driveways.