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Old 04-23-2017, 04:54 PM
DSYoungEsq DSYoungEsq is offline
Join Date: Jul 1999
Location: Indian Land, S Carolina
Posts: 12,988
Originally Posted by Riemann View Post
Yes. The numbers mean something, but they are not probabilities.
How do you know this?

The standard Prob. of Precip. that the NWS uses is confidence x coverage.

So if the NWS says that the PoP is 100% on Sat. afternoon for a given area, they are 100% confident that 100% of the forecast area will see rain at some point during the period in question.

If the hourly probability of precip that TWC offers says something like 1pm: 40%, 2 pm: 50%, 3 pm: 90%, 4 pm: 90%, 5 pm: 75%, 6pm: 30%, that should mean (assuming they agree with NWS that the coverage will be 100%) that they are not certain exactly when in the time frame involved the rain will occur. Confidence level goes up as the front's expected arrival time gets closer to what most of the models show, and drops off as time passes beyond that. Do you think that this is not true?