All about the polar cold storm freezing the United States

• Since Thursday, an icy cold storm, accompanied by strong winds, snow and blizzards has paralyzed the northern part of the United States.

• This Monday morning, the authorities of the various States recorded a total of 32 deaths in nine States.

  More than 300,000 American and Canadian homes were without power.

• 20 Minutes

  compiles for you all the information on this "explosive genesis" which is currently crossing the United States, whose exceptional coldness is linked to the sudden drop in atmospheric pressure, i.e. in less than twenty-four hours.

“I've been through every major winter storm in the last 60 years.

[…] This is the worst “, launched this Sunday

Kathy Hochul, Governor of New York State.

For the past few days, the United States has been hit by a polar cold storm, especially in the North, in the Great Lakes region.

Very strong winds, blizzards and snowfalls lowered the mercury in the plains to -31°C, or even -55°C in felt temperatures.

So far, more than 30 deaths have been confirmed in nine states.

returns to this "cyclonic bomb" which deprived more than 300,000 homes of electricity in North America.

When did this mega storm start?

On Thursday, the first effects of a storm as we only see it "once in a generation" were felt in a large part of the United States.

Faced with the desire of millions of Americans to join their families for the holiday season, the authorities have called for calm and to stay at home.

"Please take this storm extremely seriously," President Joe Biden urged Thursday.

I encourage everyone (…) to listen to the warnings at the local level.

»

At dawn on Friday, more than 240 million people (more than 70% of the country's population) were affected by winter weather alerts.

Since then, several northern states have declared states of emergency, such as New York, Oklahoma, Kentucky, Georgia and North Carolina.

Americans are shivering as far south as Texas.

On Thursday, the roads were already covered in snow and numerous accidents were reported by the media.

According to the authorities, snow and winds have caused blizzards in some places, making travel "dangerous and sometimes even impossible".

The I-90, a major highway crossing the north of the United States, was closed in the state of South Dakota, the authorities having warned that the trunk road would not reopen until Friday.

Amid plunging temperatures, one person in Montana decided to throw some boiling water into the air and make more snow.

The huge winter storm pummelling the US has intensified into a "bomb cyclone", with 60% of the population under a winter weather warning.https://t.co/4DalHHz9Lj pic.twitter.com/ADu80WBRKP

— Sky News (@SkyNews) December 24, 2022

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What are the human and material balance sheets?

On Monday, state authorities recorded a total of 32 deaths in nine states, including 13 in Erie County, New York State, which includes the city of Buffalo, where snowdrifts reached up to 'three meters high in places.

Some victims were found in cars and others on the street in the middle of the snow.

“It's not the Christmas we wanted,” said Mark Poloncarz, Erie County official, who fears that other deaths will soon be counted in his locality.

"There are people stuck in their cars for more than two days and others in homes where the temperatures are freezing," the official warned.

A travel ban was imposed in this region on Friday but hundreds of people still found themselves stranded in their vehicles.

Rescuers went from car to car on Sunday to see "if they found any bodies", described Mark Poloncarz on CNN.

On the material side, extreme weather conditions deprived more than 48,000 homes of electricity Sunday on the East Coast, where the bad weather had initially deprived of electricity some 150,000 American homes, according to the Poweroutage.us site.

On the Canadian side, more than 150,000 people still had no power for Christmas, especially in Ontario and Quebec.

In the air, this polar cold prevents any plane from taking off or landing.

More than 3,000 flights were canceled on Sunday, adding to around 3,500 more canceled on Saturday and another 6,000 on Friday, according to tracking site Flightaware.com.

In Houston (Texas), under the Waugh bridge, one of the bridges sheltering one of the largest colonies of the city, hundreds of bats were found on the ground, frozen.

This is not the first time that this colony has suffered the consequences of climatic events.

With 30,000 specimens a few years ago, it has already been decimated by Hurricane Harvey in 2017 and then by a cold snap in February 2021, recalls the

.

But, by the way, what is a “cyclonic bomb”?

According to meteorologists, a "cyclone bomb" would be the cause of this extreme cold wave.

Since the start of this episode, which Cyrille Duchesne, meteorologist at the Weather Channel, describes as "historic", several cold records have been broken: -53°C in western Canada, -38°C in Minnesota, but also, further south, where temperatures are usually milder at this time of year, -13°C in Dallas or -8°C in Houston.

The causes are however quite classic according to weather experts, namely a low pressure system, caused by a powerful conflict between two masses of air: one very cold from the Arctic and the other tropical from the Gulf of Mexico. .

A depression is a system of low atmospheric pressure, often synonymous with bad weather: its dynamics lead to updrafts that cause clouds and precipitation.

What makes the current case extraordinary is that the atmospheric pressure this time dropped very quickly.

This is called an "explosive genesis" (or "cyclonic bomb").

This appears when the pressure drops by more than 20 hectopascals (hPa) in twenty-four hours at mid-latitudes.

In the case of the United States, the atmospheric pressure suddenly dropped by 40 hPa in twenty-four hours, according to Yann Amice, meteorologist at Weather'n'co.

This is the same phenomenon that was at the origin, in France, of the 1999 storm that has remained in memory, or of Xynthia, in 2010. "This led to the formation of extreme storm conditions near the heart of depression, with particularly harsh conditions", marked in particular by winds of up to 80 km / h, blizzards and snowfall, says Cyrille Duchesne.

Cold start to Christmas Eve in the #US & #Canada, temperatures all the way down to the #Gulfcoast below freezing with low single figures even as far south as central #Florida, adding on the windchill and it feels into the negative figures, with -50s further north!

#BombCyclone ❄️ pic.twitter.com/sLn4nIIniY

— WEATHER/ METEO WORLD (@StormchaserUKEU) December 24, 2022

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For the latter, the rarity of this storm does not come so much from its causes - a "low pressure bomb, it happens regularly" - but from its intensity and the extremely low level of temperatures: "That's what makes it is exceptional”.

What is this due to?

Quite simply to the fact that the storm causes a plunge in the polar vortex, that is to say a particularly cold mass of air coming from the Arctic, towards the temperate latitudes, carried by the undulation of the

(current altitude) and favored by anticyclonic conditions on the Pacific.

Result: sometimes vertiginous drops in temperature have been observed, as in Denver where the thermometer lost 33 degrees on Thursday in just seven hours, recording with -31 degrees its lowest temperature since 1990. Combined with the blizzard and the snow, the feelings in the plain can sometimes reach -55 degrees.

How long will this episode last?

This weekend, the depression, located at the level of the Great Plains and the Great Lakes before the Christmas weekend, moved towards Quebec during the weekend.

Monday morning, in its bulletin, the National Weather Service (NWS) indicated that "much of the eastern United States will remain subject to severe cold through Monday, before more moderate trends on Tuesday" and even speaks of a return “to seasonal normals by the middle of next week”.

In the meantime, the American authorities invite the inhabitants of the Northern States to always not move to avoid accidents because of the thickness of the snow which is still very important over a good part of the territory.

"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 US National Weather Service.

And this makes any movement “dangerous or even sometimes impossible”.

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