This scenario is among the most feared in French orchards and vineyards. After a very warm winter and start to spring, the cold has set in in France since April 15. Already very marked, it should further intensify in the coming days. Consequence: a more or less massive frost episode is not excluded. “This freeze being multifactorial, it is very difficult to anticipate its occurrence”, warns agroclimatologist Serge Zaka on X. However, the risk is there, and it is relatively significant.
Polar air masses…
This risk of frost is primarily due to the cold air masses which, over the coming days, will continue to descend into the French sky.
“The anticyclone will be well established over the British Isles and will control a flow from the North, which will start from the 60th parallel, descend towards Norway, the North Sea then the English Channel, and will bring cold air to France” , explains to West France Yann Amice, meteorologist for Weather & Co.
…and clear skies
The possible occurrence of frost will also be favored by the fact that the night sky should be relatively cloudy over the coming days.
Clouds indeed play a very important role in defining the minimum temperatures observed at the end of the night. When they are present, they allow some of the heat that the ground releases at night to be retained in the atmosphere, after having stored it during the day. On the other hand, when there are no clouds, this heat is evacuated more directly into the upper reaches of the atmosphere, which results in colder ground temperatures. This phenomenon is also reinforced when the wind is weak, as will be the case in the coming days.
The northern half, the Grand Est and the very exposed massifs
This risk of frost will materialize from this Friday, April 19, for several days. “We will be exposed as long as we are under this cloudy northeast flow”, explains Yann Amice. Frost, more or less intense, could therefore potentially be observed until the last days of April, even if certain days, such as Wednesday 24, seem less risky.
This episode of frost should especially be significant in the North, East and center of France, including the central massif. “We will be a little less exposed on the coastal edges”, explains Yann Amice. The inertia of the ocean (whose temperature changes less quickly than that of the land) and stronger winds are the main causes of this less cooling.
This pattern is particularly visible on the map below. Based on data from the European model, it presents the minimum temperatures expected on Tuesday April 23 in the morning. Areas where minimum temperatures are around 0°C are displayed in turquoise green or pale blue.
Significant agricultural consequences
While, encouraged by the heat of March, vegetation has begun to develop, these hypothetical frosts could have significant consequences for winegrowers and arborists in the affected regions. “A cold phenomenon at the start of vegetation is what is most dangerous, because the vegetation has not had time to strengthen and it is then very very fragile”notes Yann Amice.
“Depending on cloudiness, wind and phenology (date of appearance of buds, editor’s note), there is a non-zero risk of total loss of harvest due to accumulation of nights of frost”explains agroclimatologist Serge Zaka on X.
“On very advanced vegetation, the p potential loss will be significant even with light frosts…”confirms on X the Météo Center association.
“The wines of Beaujolais, Champagne, Burgundy, but also the arboriculture of Limousin, the western foothills of the Massif Central and all high altitude zones are currently particularly at risk”concludes Serge Zaka.
