Violent thunderstorms struck Corsica and parts of Italy

By Vesa Nietosvaara (EUMETSAT) and Ivan Smiljanic (Exostaff)

The storms developed extremely rapidly in the morning, sweeping across Corsica and moving to northern parts of Italy in a matter of just a few hours. Violent gusts accompanied the storm clouds, with gusts up to 60m/s on the western coast of Corsica.

The Meteosat-11 Airmass RGB and H SAF precipitation product animation (Figure 1) show how rapidly the development took place in the morning of 18 August. The system was embedded in cold front associated with a low pressure system that moved across France towards the Genoa bay (Figure 2).

The animated satellite imagery (Figure 3) reveals rapid advection of convective storms towards the north east and vivid dynamics on top of the storm clouds — overshooting tops, gravity waves and radial cirrus clouds (Figure 4). Such cloud top features are only really resolved at higher spatial resolutions, in this case with nominal 1km of the High Resolution Visible (HRV) channel from the SEVIRI instrument. Even higher spatial resolution of scanning will be available with the upcoming MTG mission.

Regions of most intense vertical motions are best seen with the Convection RGB (Figure 5). Due to high vertical speeds inside storm updrafts, ice particles have less time to grow before reaching the cloud top. This microscopical signal is shown in yellow shades on the Convection RGB.

A similar process of small ice particle formation can also happen with cloud anvils that raise quickly, due to a strong storm dynamics at tropopause level. The sandwich product (HRV channel and Convection RGB combined) can best show these small particle size anvil regions (again, in yellow shades), occurring on the upwind side of the cloud (Figure 6).