A preliminary study of the synoptic conditions associated with lightning flashes over Mt. San Salvatore, Lugano, Switzerland

A preliminary analytical study has been made of the synoptic situations associated with thunderstorms that initiate upward-moving leaders from the towers on the Mt. San Salvatore near Lugano, Switzerland. Synoptic situations at the time of the lightning occurrences were divided into six categories based on the surface weather and flow pattern during the period 1967–1969 at Lugano. Cloud thicknesses were estimated from the LFC (Level of Free Convection) and LCL (Lifting Condensation Level) from the mean sounding at Milan. Large cloud thicknesses were found to be associated with the combined upward and downward discharges and smaller cloud thicknesses were associated with only upward discharges (flashes initiated by upward moving stepped leaders). Furthermore, the large cloud thicknesses were associated with the thunder-storms that had proportionally more flashes to the surrounding countryside than to the tower itself. We offer the speculation that the difference in upward and downward discharges to the towers with associated synoptic situations may be explained on the basis of a deficiency of large raindrops which are believed to be necessary for the initiation of downward discharges.