2023-06-15 11:57:42
Given the heat wave currently hitting the country, this “cold hole” phenomenon is not going unnoticed.
The causes of this nocturnal frost in the Ardennes are clear skies, dry territory and little wind. “The most important cold hole in the Benelux was then able to function optimally,” writes Noodweer. Temperatures also nearly dropped below zero in Mürringen, east of Bütgenbach, and Braunlauf, south of St. Vith. At the same time, on the highest point in Belgium, the Signal de Botrange, the mercury only dropped to regarding ten degrees.
A “cold hole” is a place, often in a steep-sided valley, in which, under certain weather conditions, cold air can accumulate and nighttime temperatures drop. This phenomenon is formed in case of weak wind and clear sky. During the night, the air at ground level becomes colder than the air above. Cold air is more compact and heavy than warm air and always seeks the lowest position due to gravity. This explains this drop in temperature in the valley, most often on a low slope. Also, dry ground cools faster than wet ground.
Bütgenbach is Belgium’s most famous “cold hole”. This place is located in a high altitude valley surrounded by the peaks of the Hautes Fagnes. The cold air gathers there around two villages. “People sometimes call this region Belgian Siberia,” reports Noodweer.
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