Did you get wet going home from school today? I took the picture just after the downpour this evening. It was this type of massive cloud, known as a cumulonimbus, that was responsible.

Sudden downpours like that which we experienced today often occur on hot days. The sun heats up the earth’s surface, and in turn the earth heats the air above.
The heated air is less dense so rises rapidly.  As it rises, moisture in the air condenses in to tiny droplets forming towering cumulonimbus clouds like the one in the picture.  These clouds  can sometimes stretch up to 10km high.

Eventually the drops of water become big enough to fall to earth and we get soaked. Thunder and lighting is common with this type of rain.