Comparison of Traditional and Newly Developed Thunderstorm Indices for Switzerland

Abstract

The preconvective environment on thunderstorm days in Switzerland north of the Alps has been investigated during a 5-yr period (1985?89). Thermodynamic and kinematic parameters calculated from the radiosounding in Payerne (started at 0000 and 1200 UTC) were used to characterize the initiation of convection. The best parameters were evaluated by using three methods: 1) skill scores, 2) probability distributions, and 3) mean temperature soundings and hodographs. For the decision whether a thunderstorm day was expected or not, the best results were obtained at 0000 UTC with the original Showalter index and at 1200 UTC with the SWEAT index. In addition, to decide whether an isolated or widespread thunderstorm day was expected, the most successful parameter was the modified CAPECCL. Furthermore, the best thermodynamic and kinematic parameters were combined to create new thunderstorm indices, similar to the calculations of the SWEAT index in the United States. The new thunderstorm indices especially designed for northern Switzerland were jointly called the ?SWISS index? (combined stability and wind shear index for thunderstorms in Switzerland). All of the traditional and new indices were verified with independent data from 3 yr (1990, 1992, and 1993), showing the best results for the new combined indices.