Extreme temperatures, strong winds…what is this “cyclonic bomb” paralyzing the United States?

Blizzard, high winds, heavy snowfall and expected temperatures reaching -55°… Since Wednesday, Canada and the United States have been hit hard by a major winter weather event that should last until the end of the week – the end of Christmas.

“Please take this storm very seriously,” even Joe Biden warned on Thursday. The President of the United States called on his fellow citizens to “heed the warnings at the local level.”

In its latest bulletin, the US National Weather Service describes a “historic winter storm that will cause widespread destruction” in the country. It mentions “more than 200 million people, or approximately 60% of the American population” affected by the riots. Several states have declared a state of emergency: New York, Oklahoma, Kentucky, Georgia or North Carolina.

Trench from Canada to the Gulf of Mexico

So at the heart of this phenomenon is this “cyclonic bomb” or “low pressure bomb”, originally “due to what is called the sinking of the polar vortex,” points out Cyril Duchen, a meteorologist at La Chaine Météo. Specifically, especially cold air coming from the polar zones flows south over the North American continent, driven by a powerful air current. jet streamupper air current.

“This is a depression that deepens very quickly, which is associated with bad weather and air mass conflict: cold air that descends from the polar zones collides with warm air that rises from the Gulf of Mexico to the eastern United States,” the expert adds. And in continuation: “We are talking about a depression bomb if depression loses more than 20 hectopascals in 24 hours, and this applies to this episode.”

What is also impressive in this case is the scale of the phenomenon: from Canada to the southern United States and the Gulf of Mexico. “We are approaching low temperature records in Texas, for example, with -12° in Dallas or -8° in Houston,” explains Cyril Duchen.

This Friday, the riots mainly touch the center of the United States and the Great Lakes region, and then rise towards Quebec and Newfoundland. Finally, the northeast of the United States and, in particular, the state of New York will suffer, ”adds the expert. The Big Apple should be back under a good layer of snow by Christmas, even if the depression gradually eases by the end of the weekend. The New York weather service is reporting wind gusts of 70 to 90 km/h this Friday in the region.

By that time, extremely low temperatures should be recorded. The latest National Weather Service forecasts for this Friday at 13:00 are -33° Celsius in Chicago, Illinois, -22° in Detroit, Michigan, or -29° in St. Louis, Missouri.

Thousands of flights canceled in the US

As a direct consequence of this exceptional meteorological episode, air and road traffic has been severely disrupted. Thousands of flights continue to be canceled this Friday, according to flight-tracking website FlightAware. 188 flights depart from Seattle Airport, 160 from Detroit and 147 from Chicago.

Caution is also on the roads, where, according to the American Automobile Association, 102 million Americans still need to use their car to get to their venues. On social media, images posted in recent hours show severe traffic problems.

Last January, a similar but less intense episode had already plunged more than 95,000 homes into darkness. Due to heavy snowfall – 60 cm, for example, in Boston – and strong winds, the electricity was cut off. Similar incidents may occur in the coming hours.