At a time when weather conditions remain unstable in part of France, disruptions caused by what is called a “cold drop” are expected between Monday and Friday, causing violent storms and incessant rain.
Uncertain weather until Friday. At the start of the school year, Météo-France is forecasting a new mass of cold air, isolated in the middle of another even larger mass, suggesting the appearance of a particularly unstable cold drop during the week, starting this Monday.
“At altitude, we have a cold drop zone, it is a zone of low pressure at altitude and fairly low temperatures, which brings a lot of rain. This disturbance is followed by a trailing sky”, a zone of bad weather combining rain and strong winds, Météo-France explained to CNEWS last April.
Concretely, a cold drop is a pocket of cold air that appears at an altitude of more than 5,000 meters and can extend between a few dozen and a thousand kilometers.
A phenomenon difficult to predict
When it positions itself over a geographical area, the cold air mass will then come to destabilize the air mass which is on the ground. This “conflict” often causes disturbed weather, with showers, sometimes composed of sleet down to the ground, associated with strong gusts of wind.
Therefore, when there is a crossing between the air masses at altitude, where the temperature is around -15 to -20°C, and the air masses on the ground, which can vary between 20 and 25°C, the arrival of showers is accelerated. And these are often accompanied by strong gusts of wind. This “shock” can also generate upwellings of milder and more humid air from the Mediterranean.
However, according to France Weatherit is sometimes difficult to predict “cold drops”. “The trajectory of these isolated systems, which control the general circulation, is sometimes difficult to understand by weather models, which makes it difficult to predict sensitive weather,” the French meteorological service further explained.
All the more so since, starting Wednesday, Météo-France is indicating, this Sunday evening, a confidence index of only 2 out of 5 for its forecasts. It even drops to 1/5 beyond that.