Forecaster Météo France warned of a “very intense peak of heat” in much of France, and issued the orange heatwave warning to the departments of the Ardèche, Drôme, Isère, Rhône, Savoie and Haute-Savoie.
Today, temperatures are expected to reach 34-38°C in the afternoon, and up to 39°C in some areas. On Friday, the mercury is expected to rise as high as 40°C.
This will be “a level close to the records reached in July 2019”, Météo France said.
Temperatures are expected to remain high even at night, with “[Friday] night set to be hot, perhaps even more than the night before”, and "in the Rhône valley, we are expecting 22-24°C at night", the forecaster warned.
It said that the heat would remain on Saturday and the next night, “before a cooldown begins in the daytime of Sunday”. Temperatures are expected to drop by a sharp 5°C at the weekend.
This means that for most the country, the "canicule" (heatwave) is more likely to be described as a "pic de chaleur" (heat peak), as a heatwave is only technically declared when the heat lasts for three consecutive days, including staying higher than 20°C even at night.
Hot weather in France is often due to hot air being pushed northwards from the Sahara Desert, passing across Spain first.
Jean-Yves Choplin, forecaster at Météo France told news service FranceInfo: "This time, the hot air is coming from Spain, and is crossing the Pyrenees before stagnating in an 'anti-cyclone'. That is why it is particularly hot in the Rhône valley."
Mr Choplin added that the continued heatwaves are very likely due to global warming.
He said: "If it was an isolated phenomenon, we could talk about a seasonal weather 'accident', as there have always been. But when phenomena like this continue - and we have seen six months above seasonal averages since the beginning of the year - the link with global warming is undeniable."
July 2020 has been one degree hotter than average, but the summer has not yet reached the heights of the 2014, 2018 or 2019 heatwaves. Last year temperatures were the third-hottest on record, with a peak of 46 °C.
Heat in the time of Covid
The government has reminded people to be safe during hot weather - including staying hydrated, avoiding too much alcohol, checking up on friends and relatives - and also to continue to stay alert to health and safety measures against Covid-19, including respecting barrier gestures and continuing to wash hands regularly.
Public health body Santé Publique France has warned that although heat can act against viruses, studies so far show that it will not be enough to keep the coronavirus under control this summer unless people continue to take care.
It has issued further advice on how to avoid spreading the virus during times of hot weather.
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