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Old 04-23-2017, 08:20 PM
Riemann Riemann is offline
Join Date: Nov 2015
Location: Santa Fe, NM, USA
Posts: 3,474
Originally Posted by Stranger On A Train View Post
This statement of probability is not like rolling dice, where the probability of getting a certain number is known with statistical certainty that a sufficient number of rolls would converge to. It is, rather, based upon the observed frequency of rain occurring with conditions similar to those predicted by the weather model, e.g. at a certain temperature, relative humidity, and warm front coming in, rain is observed to occur xx% of the time. There is some additional conditional probability from cumulative predictions of precipitation such that a day in which each hour is predicted to have a 50% probability of rain may have a cumulative probability of 60% or 70%, but it is all based upon largely empirical models and some simplified atmospheric behavior modeling.

Yup, I understand weather forecasting and what the documented NOAA/NWS probabilities mean. That isn't the issue.

The issue is that when you look at the numbers that the likes of produce, their hourly probabilities often look much too high to be consistent with the daily probabilities, i.e. they imply an implausibly high hour-to-hour correlation.

I'm open to being proven wrong, but until et al explain what they are doing and precisely what their hourly "probabilities" are supposed to mean (it's not documented anywhere that I can find), I remain skeptical.

Last edited by Riemann; 04-23-2017 at 08:23 PM.