It’s a storm like you only see “once in a generation” according to the National Weather Service (NWS), the American weather service. Since Thursday, freezing temperatures of up to -55 ° C in the Great Plains region, as well as heavy snowfall, have affected the United States. “A cold of this magnitude could cause frostbite on exposed skin within minutes, as well as hypothermia and death if exposure is prolonged,” warned the NWS.
More than 5,500 flights have been canceled and 24,000 delayed, according to flight tracking site FlightAware. And this, while tens of millions of Americans have to hit the roads and go to airports for the holiday season. Several states have declared states of emergency, including New York, Oklahoma, Kentucky, Georgia and North Carolina. Even Texas, to the south, is affected.
“Please take this storm extremely seriously,” urged President Joe Biden. “I encourage everyone to listen to local warnings. This is serious.” “Several secondary roads are currently listed as impassable road […] travel on the road segment is physically impossible due to deep snow and widespread snowdrifts,” the South Dakota Transportation Administration said on its website Thursday. customers are without power in the United States and Canada this Friday.
Explosive cyclogenesis
John Moore, meteorologist and spokesman for the National Weather Service, said the conditions for a cyclonic bombshell were in place over the Great Lakes, where freezing arctic air from the meanders of the polar vortex met air very hot in the east, report it New York Times. The cyclone, whose pressure is likely to match that of a Category 2 hurricane, could cause snowfall of half an inch (1.3 cm) per hour, the weather service said, resulting in ” land and air travel dangerous, even impossible” until the holiday weekend.
Storms can form when a low pressure air mass meets a high pressure mass. The air then changes from high pressure to low pressure, creating winds. What defines a cyclone bomb is how quickly the pressure drops in the low-pressure mass – by at least 24 millibars in 24 hours – making the winds stronger. This process of rapid intensification has a name: “bombogenesis” in English or explosive cyclogenesis.
In the United States, the atmospheric pressure dropped to at least 862 millibars, while elsewhere it could reach 1047 millibars. “It’s a very steep gradient,” says John Moore. As the arctic front (the area where the two air masses meet) moves north and east, the conditions for explosive cyclogenesis should continue to move as well, according to the meteorologist. But as arctic air spreads over most of the country, it will eventually warm up, reducing the pressure difference and dissipating the storm. Above-average temperatures are expected across most of the country next week, John Moore said.