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Rick P.
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Voodoo huh? That's how we do things back in the world of weather! Kidding! This is all about the POP or the Probability of Precipitation. Your brother is wrong by the way, so that part of the bet is settled.
When you see a "30% chance of rain" in the forecast for a given day, it means there's a 30% chance that rain will fall in the forecast area at .01 inches or more. If you are in one town that gets that rain, the forecast has been verified. Forecast chances are based on the confidence of the forecaster who is working. While the NWS may have a 20% chance on a day in the forecast, we here at KSL make our own forecasts, so if we disagree, the forecast chance for rain may be higher.
We obtain our forecast data from the government but each forecaster interprets that data to the best of his or her ability. Usually we're all pretty close in agreement but there will be times where we aren't.
Averages are just used for almanac information, just historical look ups. Because weather is so changeable, rain happening 10 years ago on a particular day, isn't necessarily likely on that same day 10 years later.
Answered by KSL Meteorologist Dina Freedman.
