CIARA storm balance: 219 km / h in Corsica and 165 km / h in Cotentin

Through Gilles MATRICON, meteorologist
Posted on 09/02/20, updated on 12/02/20 at 07:29-
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The CIARA storm swept across a large northern third of France between Sunday February 9 and Tuesday February 11. It then unleashed on the Alpes-Maritimes and Corsica. Here is the final assessment of this storm.

This winter storm was linked to the presence of an imposing low pressure system on the North Atlantic, which was propelled by a violent Jet stream (high altitude winds blowing around 10,000 m) to the British Isles and then to northern Europe, hence the bad weather that has occurred.

A very tight pressure gradient at the surface

This vast low pressure system came to oppose a very powerful anticyclone over the Azores and Spain. The contact zone between these two action centers passes through the north of France. Thus, on Sunday, the pressure gradient was very significant with 1000 hPa in Cherbourg against 1030 hPa in Toulon. It is this difference in pressure on the ground that partially favored the strong winds that the north of Brittany, the Paris basin, Normandy, Hauts-de-France, Grand-Est and Corsica experienced.

From 1000 to 1030 hPa. A pressure difference of 30 hPa over France this Sunday. A very large pressure difference which explains why the #vents are so violent Sunday and Monday when the # tempêteCIARA on the northern regions. pic.twitter.com/38XSCZOlX5

– The Weather Channel (@lachainemeteo) February 9, 2020

An exceptionally powerful jet stream at altitude

To these large pressure differences is added the Jet Stream which circulates at an altitude of 9000 meters. This one was remarkably fast with winds at almost 380 km / h, values ​​which however are not records. As proof, a plane which left New York on Sunday morning landed less than 5 hours later in London instead of the usual 6h30 journey. In the opposite direction, it was necessary to count 11 hours of flight, facing the strong wind.

The Jet Stream is so powerful at altitude (400 km / h) that it only took 5 hours for this Boeing to reach London from New York … Instead of 6 to 7 hours in normal times! https://t.co/MsIVZUREen

– The Weather Channel (@lachainemeteo) February 9, 2020

This Jet Stream, which precisely delimits the vast Atlantic low pressure system of the powerful Azores anticyclone, therefore reinforced the gusts of wind on the ground by energizing the disturbed system.

Up to 219 km / h in Corsica

Between Sunday and Monday, stormy gusts hit the north of France. By the sea, a gust at 165 km / h was noted at Gatteville-le-Phare in the Cotentin, a lighthouse particularly exposed and not really representative. There was also a gust at 155 km / h at Barneville, on the west coast of the Manche department.

In addition, we noted: 181 km / h at the summit of Mount Markstein (68) at 1265 m above sea level. 139 km / h in Granville (50) and Boulogne sur mer (62) 126 km / h in Belmont (67) 121 km / h in Strabourg (67), this is a monthly record, 104 km / h in Paris (and 152 km / h at the top of the Eiffel Tower).

An episode remarkable for its duration

Unlike the classic winter storms which cause strong winds for only a few hours, this Caria storm is remarkable for its duration, which stretches between 12 and 24 hours over the Nomandie and Hauts-de-France regions.

All of western Europe is affected

The British Isles also suffered this storm since gusts at nearly 190 km / h were measured in the Scottish mountain, which is certainly not a record over there. These strong winds were accompanied by heavy rains which caused floods in the north of England where it fell locally the equivalent of 1 month of precipitation in 24 hours. The Benenlux and northern Germany were also badly affected.

Winds #stormy and strong #pluies : result of #inondations are reported in the north of England. Up to 100 mm of rain has been reported in the past 24 hours in the villages and towns of Shap and Keswick. https://t.co/qxeB3x6j47

– The Weather Channel (@lachainemeteo) February 9, 2020

In conclusion, it should be noted that this CIARA storm ranks slightly above the classic winter storms while remaining usual at this time of the year. Its occurrence is once every two or three years, the latest being the EGON storm of January 2017, which had been stronger (we had then recorded 146 km / h in Dieppe, 143 km / h in Amiens and 130 km / h in Caen at the time). On the other hand, there is no correlation between this classic storm and global warming, especially since the official studies on this subject indicate: “The current state of knowledge does not allow to affirm that the storms will be significantly more numerous or more violent in mainland France during the 21st century “(Météo France).