should we expect temperatures of 45-46 degrees in France for the weekend of July 14? – Liberation

Alarm weather forecasts are circulating on social networks. But these data come from a twelve-day model that is subject to too many uncertainties to be taken literally, according to Météo France.

According to a now-deleted tweet from BFMTV weather presenter Marc Hay, temperatures in France could reach 45-46°C by mid-July.

“Really hoping the models crash! Because if we don’t, we will really be scorched on the horizon of July 15/16! 45/46 in France, over 40 in the UK! It’s really crazy! It’s still a long way off, we’ll be following the situation closely! #heatwave #heat”, he wrote on July 3 on Twitter.

These forecasts correspond to the current temperature record in France, namely 46.0 ° C, measured in Vérargues, in Hérault, on June 28, 2019.

That’s why the BFMTV weather presenter deleted his tweet afterwards.

fast, Weather France he answeredThis is just a model, and that the“We can’t imagine this is the temperature we will experience in a week”.

The map shared by Hay actually comes from the American weather model (GFS), which is used by Météo France among other models, and which produces forecast maps up to 384 hours in advance. Therefore, the map is a twelve-day forecast.

“There is no scientific meaning.”

Contacted CheckNewsFrédéric Nathan, forecaster at Météo France, explained that the “forecasting models work well up to a certain number of days. Météo France, for its part, is limited to forecasts on D + 8 or D + 9. “Although the forecasts in this case are very global and have confidence indices, because depending on the situation, it is more or less reliable”, he warned. But “Getting a forecast map from a model twelve days ahead makes no scientific sense. The atmosphere is very unstable and chaotic, we cannot do this kind of forecast at such a time”, He added.

The GFS model regenerates forecasts every six hours. One only has to look at this pattern now to understand that the predictions Hay cites are unstable. In fact, the map still predicts high temperatures, but not quite as high (45/46 degrees).

The Météo France forecaster recalled that this type of alarmist map appeared regularly: “Every year, we see the passing of this American model, among others, 14-15 days before, hurricanes of the 1999 type that never happen. Either we have nothing at all, or very small storms”. Beware, therefore, of quick predictions.

What temperatures should you expect?

What temperatures, however, should we expect in ten days? “We can’t say it won’t be hot the weekend of July 14, as the various weather patterns are all converging into a period of high heat. But more than a week in advance, we still can’t tell its exact intensity or duration. explained Frederic Nathan.

We really have to wait a few days for the models to converge more. To do this, Météo France uses several systems to forecast temperature: the American GFS and European (CEPMMT) models for long-term forecasts, and the French Arpege and German Icon models for shorter periods . The Arome model is also used for more accurate predictions.

However, “we are almost certain that it will be warm, even very hot, in the South and South-West, with temperatures exceeding 35°C”, step forward Frédéric Nathan.

Temperature “abnormalities”.

Words confirmed by Gaétan Heymes, also a forecasting engineer and snow scientist at Météo France, that highlighted that”from July 8, the air mass will warm up slowly but surely, especially from the point of view of maximum temperatures, which will rise above seasonal norms”. According to the forecaster, we should rather discuss, in this case, a “strong anomaly” of temperature.

“With this kind of anomaly, we have reached levels that are rarely reached for a long time. You have to understand that +3°C in a day is common, but +3°C in a week is even more rare”.

Regarding the 45-46°C expected twelve days ahead, he responded that “ithis numbers are scary, but [qu’]there is a high probability that the reality is still below”.

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