The recent finding that most of the global warming observed these past
decades is due to an increase of the nighttime temperature may have i
mportant implications on severe storms occurrence. Indeed, the daily m
inimum temperature which is generally recorded in the early morning is
an approximation of the wet bulb potential temperature observed durin
g 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 Fran
ce 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 co
rrelated, and the correlation gives a 40% increase in the hail damage
for a 1 degrees C increase in the mean minimum temperature.