Not a meteorologist, just a computer science guy that read a couple of papers. My understanding is that the probabilities in weather forecasts aren't a probabi

Not a meteorologist, just a computer science guy that read a couple of papers. My understanding is that the probabilities in weather forecasts aren't a probability at all, but rather a coverage measure. Local weather models are computed in discrete grid coordinates of say 10km. Every grid cell of 10km^2 has a single set of computed forecast data. The percentage is a measure of how much of that area received rain in the timeframe, not of probability of rain, but of coverage of rain.