Too hot for May. An intense and early heat wave is currently hitting France. Since the beginning of May, France has been stuck under an anticyclone and the mercury is skyrocketing. Mid-week it reaches between 30 and 34 degrees in most areas.
Some cities, such as Lyon, could exceed “at least five days in a row” the high heat threshold (30°C). “An extremely rare event in May, observed only once in a century of data, from May 16 to 20, 1945”, according to Meteo France. Are these heat exceptional? Are they meant to last? Franceinfo asked the question to Olivier Proust, meteorologist forecaster at Météo France.
Franceinfo: how to explain the high temperatures of this spring?
Olivier Proust : They are due to the transport of a mass of air extremely hot for the season from the subtropical regions, located in the northwest of Africa and off in the Atlantic. These rising air reach the Maghreb to the shores of the North Sea and the Baltic and under very high pressures. We call it a ridge, it’s a high pressure ridge that stretches from the Maghreb to northern Europe.
Are we currently imprisoned under a “heat dome”?
No. We are not in a typical heat dome situation that we experienced during the recent heat waves of 2019 and 2020 with this aspect of overheating. It is further south, in the heart of the high pressures, towards Spain, that there is this heat dome effect. Besides, it’s not an official term, we’ve been talking about it especially since the nearly 50°C reached in British Columbia (Canada) last year and we give it a bit of the definition we want.
“Heat dome or not, it’s all about the temperatures. The dome debate is like you’re discussing what brand of car is going to run you over.”
Olivier Proust, forecasterat franceinfo
In France, for the moment, we do not have an isolation of the hottest air under an anticyclonic screed with a closed air circulation. Instead, we have simply anticyclonic conditions, with extremely mild air mass transport underneath. This weather circulation will produce temperatures at the height of the records that we know on the territory in May.
Indeed, the mercury panics. Does this mean that we will experience new temperature records?
If this atmospheric circulation is not so exceptional as that, on the other hand it brings a mass of air which is extremely hot. So much so that we are close to, or even beat, monthly temperature records even though we are only in mid-May.
“Tuesday, thanks to an offshore wind, we reached 26.6 degrees at the tip of La Hague in the Cotentin (Normandy), this broke a record from 1922.”
Olivier Proustat franceinfo
If, in general, we do not care about whether we break the record at the beginning or at the end of May, breaking records from mid-May when the vast majority of these date from the at the end of May, it is more remarkable.
Does this rise in temperature mean that we have entered global warming?
Oh yes. It is constitutive of global warming to see this type of situation, namely an air circulation that is not so extreme and yet produces exceptional temperatures. This type of situation is expected to be more frequent, to be potentially more intense and to arrive earlier in the season. Moreover, global warming is observed in all seasons, where we observe the presence of warmer air masses.
Does this episode of heat augur a scorching summer?
A current weather situation does not predict a weather situation in three months. Just because we have a heat wave in May doesn’t mean we will have one in July. There is no connection between the two phenomena. For example, May 2011, the hottest nationwide on record to date, preceded a “rotten” summer.
On the other hand, it reveals that it is enough that the wind does not come from the right side to reach extreme temperatures, so it does not bode well for the summer. At Météo France, we are watching with anxiety the installation of a circulation which favors the rising air from the South and with it potential heat waves and heat waves.
How long will this heat wave last?
As of this weekend, there should be more reasonable temperatures and some hope of precipitation, not generalized, over the northern half of the country. But these episodes of high heat are expected to be more frequent, more intense, with high temperatures.