Julius Brant, age 91 of Norfolk, Mass for his question.
What happens when a cloud bursts.?
All of us have had to run for shelter from a sudden shower. Down dashes the rain, soaking everything in its path. Rainfall is measured by how many inches of it fall upon the ground. Of course, most of it either sinks in the earth or drains away in streams and gutters. Hut the record of rainfall tells us how much water would cover the ground if none of it drained away.
Maybe you think that a helter skelter shower can rain about six inches in a minute.. Actually, this would be just about impossible. It is not likely that your shower dropped more than one quarter inch of water in five minutes. Such a shower over an area of one square mile would pour down about 15,320 tons of water. The Weather Bureau rates such a rainfall as excessive and it never lasts long. One inch of rainfall 72,300 tons per square mile in an hour is also rated excessive.
The puzzle, of course, is where all this water comes from. If all the moisture in the rainiest cloud above you were to fall it could only drop one inch of water into a pail, When rain keeps up a steady downpour, it means that new damp air is being drawn into the rain making cloud. There it is chilled and formed into raindrops large enough to fall.
Once in a great while a shower breaks all records. The rain seems to tumble down in solid sheets of water, as though it were poured from a pitcher. In days gone by, people thought that these record breakers were caused by the bursting of clouds. Nowadays we know that even the rainiest cloud is no more than a foggy collection of minute droplets of water. It is not a great bag of water with small holes for spilling raindrops. Nor can it split open and drop its water with a great burst.
Though we still call these drenchers cloudbursts we know that they are caused by special conditions in an ordinary rain cloud, Sometimes such a cloud is held aloft by a strong uprising current of warm air. A warm wind, blowing straight upwards, keeps the newly formed raindrops from falling earthward. More and more raindrops are formed as new, moist air rushes into the rain making cloud
Finally the weight of the raindrops becomes too great to be held aloft by the updraft. Down they come in what surely seems like a cloudburst. Such a shower has been known to pour a whole inch of water upon the ground in five minutes. That's four times as much rainfall as from the helter skelter shower Lucky for us, a cloudburst does not happen very often, What’s more, it never spreads over a very wide area