Torrential rain, scorching temperatures, extreme gusts of wind: when a meteorological record falls, it is rare that it goes unnoticed. Impossible however that you felt directly the one which was reached this Monday in several weather stations of the northern half of France: the atmospheric pressure, that is to say the pressure exerted by the air on the ground, reached peaks. Little known to the general public, this phenomenon is nevertheless crucial in meteorology.
The good and the bad weather - the big question that teases us all, let's be honest - are in fact the product of a waltz that is constantly dancing above our heads in the so-called low pressure areas - the depressions - and areas high pressure - anticyclones. In the former, lighter warm, moist air prevails, which tends to rise. By meeting cooler masses, it "releases" its heat and humidity, giving birth to clouds, thunderstorms, in short: in rotten weather. Conversely, in highs, cold and dry air prevails, it is heavier, descends and drives out bad weather.
No direct health impact
And so it is precisely an anticyclone, positioned in a rather original way in the south of England, which has generated in recent hours a surge in atmospheric pressure. "It is a thermal anticyclone, typical in winter even if this level of pressure is quite rare", confirms Frédéric Decker, forecaster at Météo News. In several places, on the Normandy coasts and in Hauts-de-France, the pressure reached 1049 hPa (hectopascals), thus beating the previous record approved by Météo-France since 1951: 1048.9 hPa recorded at Saint-Nazaire, on 3 March 1990. In reality, the real national record was not broken: it had been recorded on February 6, 1821 at the Paris observatory - the station of Montsouris did not exist then, and Météo France neither - with 1050 , 4 hPa.
Anyway, several stations in the northwest of France, but also in England and Belgium, undoubtedly around or beat their record on Monday. Do not worry, at this level, the pressure has no direct effect on health. "In winter, the only concern with this type of phenomenon is that it causes pollutants in the cities to settle on the ground and can accentuate pollution episodes, there should be one later this week", nevertheless warns Frédéric Decker. Until then, the only manifestation of this pressure stroke is this radiant sun which should reign alone in the sky of the north of the country all this beginning of the week.