Dear Tom,
If there were a coffee cup sitting on the pool deck and we got an inch of rain, would the water levels in the pool and cup both go up by one inch? Joe Wood, Braidwood, Ill.
Dear Joe,
If all the water that falls during a one-inch rainstorm were to accumulate instead of soaking in, running off, or evaporating, a blanket of water exactly 1.00 inch deep would cover all horizontal surfaces. The water levels in your pool and cup would both rise by exactly one inch.
But take care: The “collection area” into which rain falls must equal the flat-bottomed gathering area into which the rainwater accumulates. Only in this way will the cup preserve a precise one-to-one ratio between the actual depth of rainfall and the depth of water that you measure.
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
WGN-TV meteorologists Steve Kahn, Richard Koeneman and Paul Dailey plus weather producer Bill Snyder contribute to this page.
