• Since Monday, the famous vigilance map of Météo-France, which warns of a possible danger, also concerns the next day.

  • Maps of areas exposed to avalanches and the risk of waves-submersion are also refined so as not to panic an entire department.

  • On average, the vigilance system detects 98% of extreme events and produces 14% of false alarms for phenomena that ultimately do not occur, or at least not in the planned zoning.

Who hasn't warned a loved one or mentally recalculated their schedule and trips when they saw a department turn orange, or red, on the famous Météo-France vigilance map?

Since its first appearance in 2001, it has signaled in anticipation more than a thousand extreme phenomena.

Storms, violent winds or heavy snowfalls at the start, then heat waves and cold spells in 2004. In 2011, the risks of flooding and flooding waves enriched its palette.

The idea, from the outset, and thanks to the inevitable spiel on the "behaviours to adopt" that accompanies it, is not only to warn as widely as possible but also and above all to allow the authorities to preposition relief and to get organized.

Except that so far, the famous map – which the most anxious or keen on forecasts know that it is traditionally updated at 6 am and 4 pm – only distilled its warnings on “24 rolling hours”.

Since Monday, she has seen further, “until the next day”, indicates Véronique Ducrocq, the director of forecasts, leaving 24 hours more to anticipate.

Which is not a luxury, at a time when global warming is causing extreme weather events to rain.

Technically, on the site, you have to click on the "tomorrow" tab, at the top right, to display the bonus card.

"Don't Cry Wolf"

Those who remember the disastrous episode of the storms of August 18 in Corsica, which was not the subject of any anticipated vigilance, could be tempted to sweep this evolution out of hand.

"It wouldn't have changed anything," says Véronique Ducrocq.

In this case, we had no elements of anticipation before the first observation on the Corsican coast of the occurrence of this exceptional event”.

And usually, the vigilance system is quite reliable.

According to the evaluation carried out by Météo-France, the rate of “detection” of episodes of heat waves and extreme cold is 100%.

It fluctuates between 97% and 99% for thunderstorms, ice and snow, then drops to 93% for high winds, “the most difficult to predict”.

For the year 2021, during which 66 episodes of orange or red vigilance were activated, the rate of “non-detection” of phenomena was 1.7%.

There were also 14% of “false alarms”, announced phenomena which did not take place.

Like this year the storms which were to break out on the evening of the Fête de la Musique, leading to cancellations, and which finally passed offshore.

“We had complaints.

But we can't cut it.

If we want to have effective vigilance,

you have to accept false alarms in order to be able to manage a risk that can prove to be problematic.

Otherwise ;

we would have more missed events,” explains Benoît Thomé, regional director of Météo-France in Rhône-Alpes.

“The difficulty is not to cry wolf.

Most often, false alarms are due to an excessive extension of the zoning of the event”, specifies Véronique Ducrocq.

Refined zoning

The other evolution of vigilance concerns the risks of avalanche in the mountains or waves-submersion on the coasts.

They led so far to place all the departments in yellow, orange or red while only mountain ranges or coastal strips were concerned.

This will always be the case on the generic card, posted on Twitter in particular.

But on the site, by clicking on the departments then on the tabs of these two phenomena, the zoning becomes more precise.

Experiments are underway to extend this finer resolution to areas affected by strong winds (mistral, autan and tramontane) as well as by snow-icing or rain-flooding phenomena.


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