Heat: felt heavier and more uncomfortable for the next few days

Of Cyrille DUCHESNEmeteorologist

The heatwave that began last Monday marks a brief lull over a large northwestern half on Thursday and Friday with the arrival of cooler air from the Atlantic. The heat will intensify this weekend and into early next week, with a feeling quickly becoming heavy and uncomfortable.

This week France is experiencing afternoon temperatures that are 5 to 8°C higher than normal for the season, but this heat is combined with very dry air with a relative humidity of between 30 and 50% making it quite bearable. When this low humidity is combined with some wind, the feeling is even more pleasant. These pleasant weather conditions will give way to a wetter air mass over the next few days, which will cause discomfort.

A heavier feeling this weekend

Starting this weekend, a low associated with cold air at altitude will deepen over the nearby Atlantic as the anticyclone installed in France shifts toward central Europe. Before the Atlantic low, an unstable south-south-southwest current will gradually develop. So more humid air may seep in over a northwest third over the weekend and stop early next week. The heat in combination with the high humidity of the air mass (70-80% relative humidity) causes an uncomfortable feeling, intense heat and in combination with the circulation of small cold drops from a height, it will be conducive to the development of thunderstorms .

High humidity prevents sweating

When the temperature is high and the humidity is high (more than 70%), the perceived temperature is sometimes much higher than the actual temperature your thermometer shows.

The explanation is simple: in order to dissipate heat and maintain a temperature of 37°C, the human body sweats. However, the higher the humidity, the less the body has this opportunity. In these situations, the feeling of severe weather sets in, which will be the case in the West from Sunday. This is one of the difficulties that the athletes encountered during the Tokyo Olympics, where the very high temperatures, sometimes combined with high humidity, made it difficult for the athletes who were no longer able to relax . In India today, the intense heat that precedes the monsoons combines with increasingly humid air from the Bay of Bengal, the heat is becoming suffocating and difficult to bear.

But besides the temperature level and humidity, other parameters need to be monitored to adjust your behavior in the coming days.

Track discomfort based on perceived temperature

Wind and sunshine are also important factors. With a weak wind, the humidity level stagnates, which increases the discomfort. This will partly be the case in the next few days. After all, sunshine can also play with this concept of feeling. Therefore, the maximum discomfort occurs when all these parameters come together almost simultaneously: great heat, a lot of sunshine, high humidity and weak wind.

For this reason, our forecast service has been integrating the forecast temperature under wind protection, humidity, wind and solar radiation into the calculation of the felt temperature for several years. It makes it possible to anticipate the times of the day that are “risky” to health, especially for people exposed to the sun, to heat, for professional reasons or in connection with the practice of sport. Since each of us reacts differently in these situations due to a very personal weather sensitivity, it is all the more important to consult the forecasts of these felt temperatures for every day, but also for every hour. This way you can optimize your decisions to choose the most favorable times for your outdoor activities.

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