Jamiewx
Storm Tracker
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Posts: 371
Loc: Orlando, Florida
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Rain Chances
Thu Jul 08 2004 03:56 PM
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In case some didn't realize, when a rain chance is given in a NWS forecast, say its 50%. It doesn't mean 50% it will rain and 50% it won't, but rather the percentages represent areal coverage of precipitation. So 50% would mean that 50% of an area is expected to be covered by precipitation. I think Ed might be able to back me up on this.
Also, anyone who can obtain a copy of todays edition of the Orlando sentinel, there is a very nice picture of a lightning strike plastered right on the front and a very interesting article inside it. With recent injuries and deaths from lightning, i think the NWS and the media are trying to get a safety message out to people, especially at this time of the year.
Here is an answer to a question that the NWS gave someone, when they asked about rain chances
"What does "50 percent chance of rain" mean? A lot of people think "It's either going to rain or it isn't. I could make that good of a forecast!" That's not what we mean by a 50 percent rain chance! In order to calculate whether it will rain at a point, say at your house, there are two uncertainties that must be factored. 1) What is the probability it will rain in the area, say Brevard county today? 2) What percent of the area will receive rain if it does indeed occur? Here is the mathematical way of stating this: POP = AP x AC, where POP is the Probability of Precipitation at a point (your house), AP is the Areal Probability (Brevard County), and AC is the Areal Coverage. This equation is simplified during the summer since the AP is usually 100% (it rains most every day somewhere in Brevard county). In essence, what we forecast in the summer is the percent of coverage. To describe the rain chances in our weather forecasts, we use the following uncertainty terms / areal qualifiers: 10-20% is slight chance / isolated, 30-40% is chance / scattered, 50 percent is good chance / scattered, 60-70 percent is likely / numerous. Rain chances of 80 percent or higher are not given an uncertainty term or areal qualifier...in other words, expect rain! "
Edited by Jamiewx (Thu Jul 08 2004 04:13 PM)
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