Analysis of mesoscale convective systems with hail precipitation

Severe thunderstorms hit the Ebro Valley (Northeastern Spain) during the summer months, and hail precipitation is frequently registered. In this area, the spatial scale of storm cells is usually of 10 to 40 km. Nevertheless, in conditions of deep convection there may be precipitation systems on spatial scales from 40 to 500 km or larger. These types are known as mesoscale convective systems (MCS). Occasionally, there are long-lived mesoscale convective systems, termed mesoscale convective complexes (MCC), that cause intense precipitation and may produce hail. There are middle latitude classification criteria used to identify MCS and MCC from enhanced IR images, which may be derived from METEOSAT. aper presents an analysis based on a classification of METEOSAT images for hail events in the Ebro Valley. The database consists of 72 of these hail events including 28 cases of MCS and 5 of MCC. In the remaining 36 cases, the convective air masses produced hail precipitation, but did not fulfill the classification criteria to be considered MCs. ition, the paper includes a characterization of preconvective conditions according to different sounding variables. A logistic regressive analysis has been applied and the results show the difficulties encountered in forecasting the formation of MCs on the basis of preconvective variables.