What does 40% chance for rain mean?

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What does 40% chance for rain mean?

By Jeff Rucker

Story Published: Sep 12, 2007 at 11:28 PM EDT

Story Updated: Sep 13, 2007 at 4:20 PM EDT

The chance for rain is truly a computer model, statistically derived probability that the atmosphere will produce rain over a given period of time at a given location. On our 7day forecast, we are loosely forecasting for the metro Aiken-Augusta region over about a 12 hour period.

So if we have 40% chance for rain Saturday, this means there is 40% chance the atmosphere will produce any amount of rain during the day in our area. It does not mean 40% of the area gets rain, nor does it mean it will rain 40% of the time. It also infers nothing about the amount of rain.

Our computer models provide statistical guidance for probability of precipitation over many different time periods. We try to improve the probability using our knowledge of local weather regimes and computer model weaknesses.

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Wednesday, Apr 22 at 10:42 AM Gale Wiley wrote ...

what a waste of information. I want to know at a 40% chance of rain... how often does it actually rain ??

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