The temperature goes from 5°C to -20°C: what is a cold hole, this phenomenon of extreme temperature drop

Qu'est-ce qu'un trou de froid ? ILLUSTATION UNSPLASH/INFOCLIMAT – Pascale Amez/Infoclimat

Dans la nuit du 15 au 16 janvier 2024, des trous de froids ont été recensés en France. Véritables trous noirs thermiques qui aspirent la chaleur, ces zones éparses ne font rarement plus de quelques kilomètres de diamètre. 

Over the past few days and the cold episode that has crossed France, "cold holes" are observed on both sides of the country. These areas of a few kilometers in diameter are real thermal chasms: the cold accumulates there until reaching temperatures that are explosive to say the least. 

The conditions to be met

Cold holes "are places, often deep valleys in which, under certain weather conditions, cold air can accumulate and nighttime temperatures drop below -20 °C. We find these cold holes in all of our massifs", explains Météo France.< /p>

Quel GRAND écart en France ! En ce moment, il fait :
-10.6°C à Baerenthal dans le nord-est
+20.3°C à Oloron au pied de Pyrénées !

Ce n'est pas tous les jours qu'on diffusera une carte pareille ! pic.twitter.com/dva4QjbNxn

— Asso Infoclimat (@infoclimat) January 16, 2024

"These are areas generally far from any sea or ocean, giving them a semi-continental climate. This cold tendency is reinforced by the altitude", specifies the weather forecasting organization. 

Cold holes are formed at night, when the sun is no longer there to cause the mercury to rise: & quot;the air located at ground level becomes colder than the air higher up: this is called a temperature inversion.  The surface temperature of the ground gradually decreases throughout the night and the air in contact with this cold ground in turn cools".

Up to 20° C temperature difference

Concretely, and in the space of a few kilometers as the crow flies, the temperature can drop by 20° C. The presence of snow on the ground, the absence of vegetation or the location of "combes" – kinds of cuvettes – at altitude, favors the appearance of the phenomenon. 

Significant temperature differences are observed. CLIMATE INFO

Several areas in France, and its neighbors in Switzerland, are known for their cold holes: Mouthe, Combe du lac de Lamoura, Combe des Cives in Chapelle des Bois, the Grandvaux plateau, the Maîche plateau… 

For example, on the night of January 15 to 16, – 20° C were recorded in Bouvante, in Drôme. 15 kilometers away, in the commune of Peyrus at the same time, it was only – 0.6° C.