"
We only see this once in a generation
", "
historic cold snap
"... The United States is facing heavy snowfall and polar temperatures as Christmas approaches.
Several cold records have thus 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.
Snow falls on Broadway, a popular tourist street in Nashville, Tennessee, on December 22, 2022. SETH HERALD / AFP
"low pressure bomb"
The causes of such a phenomenon, called “low pressure bomb”, are however quite classic.
They are due to 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.
The intensity of such a reaction is made historic, however, by freezing arctic air.
A man uses a snowblower to clear a sidewalk during a winter storm ahead of the Christmas holidays, outside Union Station in Chicago on December 22, 2022. KAMIL KRZACZYNSKI / AFP
The extraordinary nature of this weather is also due to a rapid and significant drop in atmospheric pressure in less than 24 hours.
This same phenomenon, called "
explosive genesis
", had been at the origin, in France, of the storm of 1999 and of Xynthia in 2010.
“
This led to the formation of extreme storm conditions near the heart of the depression, with particularly harsh conditions
”, marked in particular by very strong winds, blizzards and snowfall, indicates Cyrille Duchesne, meteorologist at La Chaîne Weather report*.
Pete, a 41-year-old homeless man, stands next to the donated tent near the freeway where he lives, as temperatures drop below 50 degrees F, December 22, 2022 in Chicago, Illinois.
SCOTT OLSON / GETTY IMAGES NORTH AMERICA / GETTY IMAGES VIA AFP
Thus, the rarity of this storm does not come so much from its causes - a "
low pressure bomb, it happens regularly
", according to Cyril Duquesne - but from its intensity and the extremely low temperature level: "
That's what makes it is exceptional
”.
Read alsoWhat is the “Extreme Cold” plan?
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 mass of particularly cold air coming from the Arctic, towards the temperate latitudes, carried by the undulation of the jet-stream (current altitude) and favored by anticyclonic conditions on the Pacific.
Pedestrians walk on a snowy sidewalk as temperatures drop below 50 degrees Fahrenheit on December 22, 2022 in Chicago, Illinois.
SCOTT OLSON / GETTY IMAGES NORTH AMERICA / GETTY IMAGES VIA AFP
A man clears his driveway of snow while a woman walks on the sidewalk after an overnight storm in Provo, Utah, December 13, 2022. GEORGE FREY / AFP
As a result, sometimes vertiginous drops in temperature have been observed, as in Denver where the thermometer lost 33 degrees on Thursday in just 7 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.
"
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
”.
A person crosses a street in Mile End, a borough of Montreal, Quebec, Canada, as snow falls on December 22, 2022. ANDREJ IVANOV / AFP
For this weekend, the depression, currently located at the level of the Great Plains and the Great Lakes, should move towards Quebec, which risks "
being very affected
" with in particular violent winds and heavy snowfalls, and to a lesser extent towards the northeast of the United States, indicates Cyril Duquesne.
People cross a street in Mile End, a borough of Montreal, Quebec, Canada, as snow falls on December 22, 2022. ANDREJ IVANOV / AFP
*
The Weather Channel is a property of the Figaro group.
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