Ann Crews, age 12, of Winston‑Salem, N. C. for her question:

What causes a cloudburst?

A cloudburst can suddenly dump 72,300 tons of water over one square acre. This is quite a wallop and luckily it does not happen very often. A real cloudburst is very rare. Sometimes we call a sharp shower in the mountains a cloudburst when it really is not. The runoff from the slopes creates such a deluge that is seems that a cloud has burst open like a paper bag.

Of course, even in a real cloudburst, the cloud does not break open. It happens because the rain forming in the cloud has been unable to fall down in a steady shower. Sometimes this happens when the cloud is ready to rain and the ground below is scorching hot. Or maybe a very warm current of air is blowing under the rain cloud. Either of these events causes a strong updraft of warm air. Raindrops find it very hard to fall through a current of rising air. When they start down, up they are whisked again,

If this goes on for any length of time, the cloud gets an overload of rain. The drops that should have fallen are returned back up and new drops are being: formed all the time. Finally something happens to change the situation. The weight of rain is able to break through or maybe the updraft suddenly stops for some reason. Then all the raindrops, new ones and old, come tumbling down at once. Truly it seems as if the rain clouds burst.