From: Steve (Primus) (Avatar) 30/10/2001 5:43:27 Subject: re: STEVE'S WEATHER FAQ post id: 476404 Also what is the signal for a raincloud to dump it's load, and do they 'rain' themselves out? Thunder is caused by lightning - it is the shock wave set up by the sudden expansion of air as the lightning heats it up. Loud thunderclaps are close by - which means the storm is close by. The rain in your area could be heralded by the thunder but it is not caused by it. I saw the lightning for some time before the storm came over. Rain will stay in a cloud until it gets too heavy to be supported by the updrafts. Very strong updrafts will produce hail which will grow to a size where it won't melt on the way down. You seldom, if ever, see large hail and rain at the same time although rain will follow the hail as the updrafts weaken. As the rain comes down, some of it evaporates taking the latent heat of evaporation from the surrounding air. The rain also produces downdrafts by friction - it drags air down with it. The combination of the air dragged down by friction and the cold dense air created by evaporation produces strong downdrafts which account for the very gusty winds which often accompany thunderstorms.