The heat wave episode in the Southwest ended early Monday evening on the Basque coast and the Arcachon basin with a drastic drop in temperatures.
This phenomenon has a name: the gallery.
It is formed by a cold wind coming from the Bay of Biscay and is accompanied by violent gusts of up to 70 km/h.
Météo France has called for vigilance because these violent and sudden winds can aggravate the fires in progress in the region.
This is a phenomenon well known to the inhabitants of the Southwest.
Galerna, or “brouillarta” in the Basque Country, causes a sudden drop in temperatures.
This is how the red alert for the heat wave was lifted this Tuesday morning in 15 departments on the Atlantic coast, after unprecedented temperature records recorded on Monday.
“A cooler ocean air mass arrived from the west”, ending “the intense heatwave episode on the Atlantic coast”, notes the Météo-France bulletin.
The meteorological monitoring institute had warned: "After a scorching day, brutal change expected in conditions on the Aquitaine coast" with a drop in temperatures to 20 ° C in one or two hours.
This sudden change is also accompanied by strong winds, up to 70 km/h.
Caution: after a scorching day, sudden change in conditions on the Aquitaine coast is expected: drop in mercury from 15 to 20° and gusts of westerly wind at 60 to 70 km/h.
Sudden phenomenon spreading from the Basque coast to the Arcachon basin between 6 and 9 p.m.
#gallery.
pic.twitter.com/xwk1LHr6y4
— VigiMeteoFrance (@VigiMeteoFrance) July 18, 2022
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What is the gallery?
"The galerne is a violent meteorological phenomenon", according to Météo France.
This phenomenon is characterized by “the violent rotation of the wind in a direction close to the west/north-west associated with a sudden increase in the speed of the wind”;
“a sudden drop in temperature and a rapid rise in relative humidity.
The temperature often drops by 12 to 15 degrees, the humidity rises by 20 or 30% towards 85 to 90%, all almost simultaneously and in a few minutes”;
“a spread from west to east (over a sometimes relatively short distance).
The weather phenomenon can also be accompanied by heavy rainfall.
Is this a frequent phenomenon?
Galerna is quite common in the south-west of the country, and more widely on the Atlantic coast.
It even has its different names depending on the region: "gwalarn" or "galerno" in Brittany, "embatta" or "brouillarta" in the Basque Country, explains Météo-France.
The gallery had already been in the news last June, during the last heat wave.
On June 18, the city of Biarritz had lost 19°C in forty-five minutes.
Enough to scare away holidaymakers who took a good sunbath on the beaches of the Southwest.
On Monday, the gallery struck again, causing tens of degrees to be lost in a few hours.
In 2019, the same thing happened in the Arcachon basin and the Basque Country where the temperature had dropped by 10 to 12 ° C in about twenty minutes, recalls Ouest France.
According to Météo-France, the galern suddenly changes the landscape three to four times a year on average and mainly from May to October.
It occurs mainly between 12 p.m. and 9 p.m.
"89% of cases of galerne in Biarritz take place in this time slot, including 43% between 3 and 6 p.m.", specifies the specialized institute.
Is it dangerous ?
While it may seem harmless, sometimes even life-saving to come and refresh the unbreathable atmosphere of the heat wave, this phenomenon is therefore accompanied by violent winds which can become dangerous.
This is why the maritime prefecture "formally" advised swimmers on Monday not to practice water sports along the South Atlantic coast.
Call for caution also for firefighters trying to control the fires that have ravaged more than 19,000 hectares of forest in Gironde.
The wind makes their task more complicated, as can be seen in videos taken by residents and posted on social networks.
Resumption of #feuxdeforet at #LaTestedeBuch #galerne #feu #fires #firefighters #Gironde pic.twitter.com/U7ueuZoaT5
— Pilou (@Pilou_Officiel3) July 18, 2022
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This wind shift has also pushed the smoke from the two giant fires northwards and since Monday evening they have enveloped the metropolis of Bordeaux, accompanied by an acrid smell.
The Department asked not to call the emergency services: “If you are afraid of breathing in the particles, put on a mask that you used to protect yourself from Covid.
We have to wait for the wind to drop”.
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