The European Windstorm Season Gets Underway With A Bang
On 30 September, the 2020-21 European Windstorm season saw its first named storm, Alex. It underwent explosive cyclogenesis, or more colloquially known as a “weather bomb,” with a drop in central pressure of nearly 40mb in 12 hours, impacting the region of Brittany in North-West France on 1 and 2 October.
A record wind speed observed on the Atlantic island of Belle- Île (west of mainland France) of 186km/h suggests that Alex may have contained a particularly hazardous feature, sometimes found within extra-tropical cyclones, known as a Sting Jet. This is a localised, cold airstream which rapidly descends from the mid-troposphere, bringing potentially very damaging winds to the surface. Owing to its relatively small footprint, a sting jet is as difficult to identify as it is to predict the possible damage on the ground.
With the exception of the record wind speed observation, the coastal weather stations in Brittany recorded windspeeds much more consistent with a high-frequency winter storm. On the ground there will be some localised damage from Alex.
As the system weakened and slowed, it advected, or transferred, significant amounts of moist air from over the Mediterranean, causing significant localised flash flooding in southeast France and northwest Italy. CoreLogic continues to monitor the impact from this event.
