SEVERE CONVECTIVE WEATHER IN THE CONTEXT OF A NIGHTTIME GLOBAL WARMING

The recent finding that most of the global warming observed these past decades is due to an increase of the nighttime temperature may have important implications on severe storms occurrence. Indeed, the daily minimum temperature which is generally recorded in the early morning is an approximation of the wet bulb potential temperature observed during the following afternoon, which is a storm predictor. A mean minimum temperature increase in a region will then probably be accompanied by an increase in thee storm frequency. This hypothesis is tested in France for the years 1946 to 1992 with the annual mean minimum temperature in summer being compared to a yearly hail severity index deduced from hail insurance data. The two elements are found to be year-to-year correlated, and the correlation gives a 40% increase in the hail damage for a 1 degrees C increase in the mean minimum temperature.