The meteorological background to this case is rather classical with a persistent cyclone over the Atlantic and a frontal system over the Iberian Peninsula. Especially in the upper layers of the atmosphere the cyclone over the Atlantic causes a continuous flow of warm humid air in the direction of Spain. In the lower layers in the beginning of the case a frontal zone is recognized over Central Spain. The NWP will later show us the unstable character of this system. Within this frontal zone already at the beginning convective cells are seen embedded. Occasionally the development of so-called V-shape storms indicate how fierce the convection is at these areas. In the small movie below the aftermath of the severe rainfall can be seen in Southern Spain.
The MeteoAlarm sites showed us in combination with the IR images where the most severe convection and highest reports of rainfall and thunderstorms where happening. The red warning showed us that this was an exceptional case. The Airmass Images also showed us clearly the presence of the jet in the upper layers which directed the warm moist air towards Spain. The set of basic parameters showed the same picture. Different structures where analyses. In the upper layers at 500 hPa a developing omega-block was seen which made certain that the depression that later developed over Spain from a Wave bulge was kept stationary ensuring a continuous setting for bad weather.
The stability of the atmosphere was studied by using the NWP fields of the Showalter index combined with the (Enhanced) Infrared, Water Vapour and Airmass satellite images. The area of maximum convection fits well with negative values of the Showalter index. With a superimposed PVA maximum this Wave rapidly develops further into an occlusion as it moves from its original position in Morocco towards Spain. Embedded into this part of the system are a range of CBs where occasionally also V-shaped structures are seen.
The VCSs show that already at an early stage the prefrontal region is characterized as very unstable. The convergence/divergence near the surface/upper layers was distinctive. A cross section through the V-shaped structure that was discussed in the chapter with satellite images revealed some severe updrafts in the fields of omega.
A final extra chapter on a F2 Tornado in Mallorca concludes this case study. This extra chapter presents the satellite and NWP material of the 4th October when a tornado swept over Mallorca. The MCS responsible for this is well monitored using the remote sensing data. The HRVIS images shows interesting features such as overshooting tops and gravity waves that depict the severity of the event. Unfortunately the range of the radar stations over the Spanish mainland are to weak to capture the whole event in detail as it moves over Mallorca but does provide some extra information due to the high reflectivity it shows. The forecast models did show the severity of this case already beforehand alarming the forecasters. The forecast fields however placed the severity further north of Mallorca.