2023-08-19 16:34:48
It is very hot all over France, and in the Paris region too. With nearly 26°C recorded around 4 a.m. that night in Paris, the mercury had great difficulty in descending on the capital. However, no department of Île-de-France is concerned by the orange heat wave vigilance, triggered for 49 others on the territory. Explanations.
Météo France defines a heat wave as “an episode of high temperatures, day and night, over a prolonged period”. Orange or even red vigilance is then activated. In the Paris region, only Paris is placed in yellow vigilance (Météo France only asks to remain attentive and to keep abreast of the situation), all the other departments are in green, therefore without risk.
“Below heat wave standards”
Why is the Paris region not concerned, since it is very hot there, even at night? Quite simply because the alert thresholds differ according to the departments. To calculate them, Météo France uses two indices: IBM min and IBM max. “The IBM (min / max) constitute the average of the temperatures (minimum and maximum) forecast by Météo France for the next three days”, explains Public Health France on its site.
To go into heatwave alert, these two figures (the minimum and the maximum) must exceed a certain threshold set department by department. For the entire Paris region without exception, temperatures must exceed a maximum of 31°C during the day, and 21°C at night. Another example, the Haut-Rhin is placed in orange vigilance (and this is the case at the moment) when the maximum temperature exceeds 35°C, and does not drop below 19°C at night.
“Even with high temperatures at night, during the day the mercury remains below scorching standards. It’s not enough to go into orange vigilance, ”summarizes Patrick Marlière, meteorologist for Agate-Météo. The problem in Paris is therefore not that the temperature drops at night – it was 26°C at 4 am – but that the mercury does not rise enough during the day. Example for the day of this Saturday, where it should not be more than 30 ° C at the peak of the day, according to Météo France.
A peak of heat until Wednesday?
Another important answer: it takes “an extended period” above these temperature thresholds to switch to heat wave vigilance. However, once again, Météo France is only forecasting around twenty degrees for the night from Saturday to Sunday in the capital, as for the next two. The tropical night of this Friday evening will remain an exception. The Ile-de-France departments should therefore not, according to current forecasts, go into heat wave orange vigilance by the end of the week. But that doesn’t mean it’s not very hot!
Cool islands, parks and gardens, fountains, open-air swimming pools, water activities in summer… There is no shortage of places to cool off this weekend in Paris! pic.twitter.com/9zoKqQDjd9
— Paris (@Paris) August 18, 2023
“It was planned in the models that the hot air lifts reach the north of France. This is the case in the Paris region at the moment. Maximum temperatures are expected until Tuesday, still around or even above 30°C. Afterwards, the weekend should end with thunderstorms to have a cooler than normal next weekend,” predicts Patrick Marlière. The episode of strong heat will therefore be short-lived, at least in the Paris region.
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