Institute for Marine and Atmospheric Research, Utrecht University - Netherlands
The formation of severe thunderstorms over western Europe is frequently connected to a forward sloping cold front which is undergoing frontogenesis. In order to bring out this feature clearly, an alternative objective indicator of the presence of a frontal zone in the atmosphere is introduced: the slope of isentropes. In the presentation I will pay attention to the advantages of the use of this indicator over the use of the traditional indicator (the horizontal temperature gradient). I will subsequently discuss the role played by several characteristic synoptic features, such as the "Spanish plume", in contributing to the intensification of the forward sloping cold front and associated with this the destabilization of the atmosphere at midtropospheric levels.