If the storms of December 1999 had deeply traumatized France, causing 92 deaths and more than 2000 injuries, they had at the time caused an electric shock to Météo France.
So much so that a year later this famous vigilance map
(yellow, orange, red)
appeared in the forecast bulletins, supposed to warn us of an imminent risk of flooding, avalanche, snow or even ice.
Twenty years later, the national meteorological services presented this Tuesday new developments in this alert system which has since proven its worth.
A forecast refined forty-eight hours in advance
In 2021, 90% of vigilance alerts were announced by forecasters at least three hours before the start of the event.
The French will now have a double card broadcast twice a day.
The first will show your department-wide risks for the current day.
The second will inform about the risks for the next day.
"It will be equipped with a chronological frieze allowing to see precisely the beginning and the end of the phenomenon which one envisages", explains Benoît Thomé, interregional director Center-East with Météo France.
“Extending vigilance alerts to the next day will allow populations to better prepare for it by postponing, for example, a trip or the practice of an exposed activity or by protecting objects around their house that would be sensitive to the winds”, underlines Véronique Ducrocq, the director of operations for forecasting.
Between 97% and 99% for snow, ice, thunderstorms, heavy rains and floods
Between 2012 and 2022, Météo France claims to have detected 100% of heat waves and periods of extreme cold in advance.
Forecast reliability drops between 97% and 99% for snow, ice, thunderstorms, heavy rains and floods.
Thanks to increasingly reliable forecasting models, Météo France will now be able to issue more refined vigilance bulletins at the level of a department for wave-submersion and avalanche phenomena.
“We can now map 46 distinct coastal areas instead of 25 previously for wave-submersion phenomena,” explains Benoît Thomé.
When an alert is triggered in Finistère, for example, three different zones will be distinguished at the level of the department, which will each have their color of vigilance depending on the phenomenon expected locally.
Ditto for avalanches, with 37 distinct mountainous areas instead of the 13 departments studied under the magnifying glass previously.
Météo France even intends in the future to refine its forecasts for the strength of the mistral or the quantities of snow expected according to altitude.
14% false alarms and 2% missed events
While forecasters no longer miss any heat wave warnings, they are less reliable when it comes to forecasting strong winds, with only 93% of successful detections in advance.
After the violent storms that hit Corsica last August, causing five deaths, Météo France found itself at the heart of the storm, singled out for not having sufficiently anticipated the extent of the phenomenon.
“Heat waves are easier to predict than other phenomena such as thunderstorms and high winds,” explains Véronique Ducrocq.
The difficulty, for very heavy precipitation, of the Mediterranean type for example, is to know exactly where the rain will fall, in what quantity and where the accumulations of water will be the strongest.
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But Météo France says it has set a rate of non-detection of extreme phenomena reduced to 2%.
And on average, forecasters issue only 14% false alarms.
“Sometimes local elected officials have taken precautionary measures for nothing, such as the cancellation of festivities this summer in view of our calls for vigilance, admits Benoît Thomé.
But you have to accept a certain level of false alarms because the forecast of a weather phenomenon can never be sufficiently precise at the location and to the nearest minute.
In other words: prevention is better than cure.