What to expect as France braces for three-day ‘heat dome’

Experts predict temperature records to fall as a well-known weather phenomenon forms over France - bringing highs more usually associated with July and August than mid-May. Here's what to expect.

What to expect as France braces for three-day 'heat dome'
(Photo: Philippe Huguen / AFP)

France basked in a late Spring heatwave last week, with temperatures topping 30C in parts of the country for the first time this year.

Now, as we enter the third week in May, forecasters are predicting that temperature records could tumble as a heat dome forms over the country.

Last week was hot, there’s no doubt, but not record-breaking – with higher figures recorded for the month in 1976, 1992, and 1998. But experts say even those highs could fall this week as a mass of hot air moves into France from the south – bringing temperatures more usually associated with July and August.

Temperatures over the weekend were already between 8C and 10C above average for the time of year – but, after a brief lull on Monday, they are set to intensify between Tuesday, May 17th, and Thursday, May 19th, as a so-called “heat dome” settles over the country. 

Weather forecast for Tuesday afternoon. Screengrab from MétéoFrance.

A heat dome occurs when the atmospheric pressure acts like a lid and traps warm air from the ocean. This trapped mass of warm ocean air produces a “dome,” like a lid on a microwave meal, inside which temperatures rise. 

The phenomenon, which occurs mainly in spring and summer, is intensified by global warming, and contributes to the increasingly high temperatures recorded year after year. It can cause, in the worst cases, droughts and forest fires.

The mercury will pass 30C across most of the country in the middle of the week, and is expected to soar beyond 35C in the south. High humidity levels mean that it may feel closer to 40C in the south west, and may lead to storms.

There will be some respite overnight, but temperatures are not expected to drop much below 20C in larger cities.

Despite the high temperatures, France’s “plan canicule” will probably not be activated this time in any department or region. 

Average temperatures across France have to cross 30 to 35C during the day and 18 to 20C at night for three consecutive days to trigger the plan – and storms are forecast across a large part of the country on Friday, pushing cooler air down from the north.

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Swathes of France placed on alert for post-heatwave storms and gales

The worst of the recent heatwave may be have passed but parts of central, eastern and north-eastern France were placed on alert on Thursday over the risk of violent thunderstorms.

Swathes of France placed on alert for post-heatwave storms and gales

Unfortunately, the severe weather in France has not quite finished yet.

Météo France placed 25 départements in central, eastern and northeastern France under the ‘orange’ alert, warning residents of the risk of severe thunderstorms this Thursday and Friday.

The départements concerned are Ain, Allier, Ardennes, Aube, Cantal, Côte-d’Or, Doubs, Jura, Loire, Haute-Loire, Marne, Haute-Marne, Meurthe-et-Moselle, Meuse, Moselle, Nièvre, Puy-de-Dôme, Bas-Rhin, Haut-Rhin, Rhône, Haute-Saône, Saône-et-Loire, Vosges, Yonne, and Territoire de Belfort.

Forecasters estimate that storms will roll in around midday and last into the night of Thursday or into Friday morning.

“These storms will could be violent,” warned Meteo France. Meteorologists are predicting locally strong hail falls, heavy rainfall -with accumulations of around 30 to 50 mm in under an hour – and strong gusts of wind, which could reach 70 to 90 km/h.

On Wednesday evening, parts of the Pays de la Loire region experienced severe thunderstorms, some of which caused damage. In the town of Le Coteau, hail caused signficant damage, with the mayor telling Franceinfo that the town was “devastated by a torrent of hail.” No injuries were reported, but there was “considerable material damage.”

Earlier in the week, France’s western départements had also been on orange alert for violent thunderstorms. 

Places like Bordeaux saw significant hail-fall, which some were able to catch on video:

Meanwhile, the orange alert for heat has been lifted for the six départements in eastern France that were still seeing high temperatures. Now, most of the south, southwest, and west of the country have returned to a ‘yellow’ alert level.