A Mediterranean derecho: Catalonia (Spain), 17th August 2003

At approximately 6:10 UTC in the morning of 17th August 2003, a squall line developed over south Catalonia (the northeast region of Spain). During the next 9 h, the squall moved rapidly northeast and crossed Catalonia and the French regions of Languedoc–Roussillon and Province, damaging and uprooting hundreds of trees and blocking trains in the region. Wind gusts reached were recoded up to 52 m/s with evidence of F2 intensity damage. This case study shows the characteristics of a derecho (widespread convectively induced windstorm). observations of the evolving squall line show signatures often correlated with damaging surface winds, including:a. hoes, nflow notches, nflow jets, altitude radial convergence, gradient of very marked reflectivity, pment of isolated cells ahead of the convective line, of convection off the northern end of the line known as a “warm advection wing”. xamining the different surface observations, satellite, radar imagery and cloud-to-ground lightning data, this case shows many similarities to those investigated in the United States. The derecho is a hybrid case, but has many characteristics of warm season derechoes. This emanates from a mesoscale convective complex (MCC) moving along a quasi-stationary, low-level thermal boundary in an environment characterized by high potential instability and relatively strong mid-tropospheric winds.