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Old 04-23-2017, 07:07 PM
DSYoungEsq DSYoungEsq is offline
Join Date: Jul 1999
Location: Indian Land, S Carolina
Posts: 12,988
Originally Posted by Riemann View Post
You have given a set of perfectly plausible numbers, if they were doing an actual calculation of probabilities.

But look at some actual numbers. Here is the forecast right now for Atlanta, GA. Convectional showery weather.

The forecast for rain at any time on Monday is 50%.

For the same period, the hourly "probabilities" are:
7am 40%
8am 45%
9am 50%
10am 50%
11am 45%
12pm 45%
1pm 50%
2pm 45%
3pm 45%
4pm 40%
5pm 35%
6pm 35%
7pm 40%

How can that possibly make sense? That could only be true if the correlation between each hourly period were essentially 1.
This is easy to decipher.

For the Atlanta area, there is 100% confidence that roughly 50% of the area will see showers. Broken down into hourly segments, the confidence remains close to 100%, and the coverage is around 50% at any given time. In other words, scattered showers are predicted with almost 100% certainty.