“It’s not the Christmas we wanted”: a winter storm, carrying icy winds and sweeping the center and the east of the United States for days, has killed more than thirty people and left tens of thousands of Americans without power on Christmas Day.
The private meteorological site AccuWeather warned last week of the formation of a “cyclonic bomb”, formed by the meeting of polar air with a mass of warmer air, causing a very rapid drop in pressure.
This winter storm is particularly impressive… Let’s explain this phenomenon with climatologist Xavier Fettweis.
What is it regarding?
“We have air that descends in a direct line from the Arctic, and as it crosses a continent which is itself cold, it keeps its temperature as it was in the Arctic. It will meet the warm air, tropical south of the United States. And this very significant thermal contrast, over a hundred kilometers, will generate very violent winds and a very dynamic cyclogenesis.”
Is it frequent?
“It happens regularly in the United States, because it is the most favorable continent. There is no sea in the North and very hot air in the South. So there is regularly this kind of thermal contrast in the UNITED STATES.”
How long can this last?
“It’s often a few days. We have a flow of cold air that lasts a few days and then this cold air will return to the Arctic where it came from.”
Does what happens in the northern United States have an influence on the weather here?
“We have the descent of cold air in the United States and to compensate for this descent of cold air, we have a south-north flow at the level of Europe which will resume very hot air. We really have a sort of loop with a descent of cold air in the United States and a rise of hot air at the level of Europe.
