Frédéric Nathan, forecastist at Météo-France, analyzes the dynamics of air masses at work in the intense cold episode which paralyzes part of the country.
By Rémi Barroux
While the United States is paralyzed with the approach of Christmas by icy temperatures and strong snowfall, resulting in a disorganization of transport in a large part of the country and many calls for prudence of the authorities, ‘Western Europe, on the contrary, records mild temperatures. Frédéric Nathan, forecastist at Météo-France, analyzes the dynamics at work in this cold wave.
The cold wave that is currently touching the United States, with particularly low temperatures, is it exceptional?
It is part of episodes that arrive from time to time. This polar cold which touches to the south of the United States is favored by the position of depression in the north. It must be understood that the solar radiation is less to the north, in the polar region, that at the level of the tropics and that, consequently, it is colder in the north. Depending on the positioning of these depressions or anticyclones, we are under the influence of polar or sub -Saharan air. This scenario is permanent and is not new.
How to explain that the current scenario in the United States does not produce the same effects in Europe?
The cold air masses that affect the United States have passed through Canada and continental land, they are particularly intense and therefore could not warm up. This explains the few records that we have observed in recent days, such as the – 41 ° C reported on December 21 in Casper, in Wyoming, a record since 1939, the first year when measures were made in this station. But, once again, the United States does not know an extraordinary situation and few records have been broken so far.
What is most impressive is the speed with which temperatures collapsed: the thermometers plunging from twenty to twenty-five degrees in a few hours. Along the rocky mountains, northeast of the country, the fall of around twenty degrees occurred in just one hour on December 22! After touching the Great Lakes region, the active center of this depression and this cold air should go to New York to then go back to Quebec, in Canada, mostly accompanied by strong snowfall.
In Europe, these cold air masses from the Arctic area cross seas, like the North Sea, in contact with which temperatures are softened.
You have 37.45% of this article to read. The continuation is reserved for subscribers.