[viraptor]

One thing I noticed recently which breaks forecasts is the size of the area. For example city forecast on wunderground may be valid for place where you have two or more stations in a suburb that's 1km across. (With lots of data points around, going on for kilometres) On the other hand, at home, my town area is closer to 10km across, has 2 stations in it and has no surrounding context.

Which means that I may have a forecast of 24h of rain which is accurate, but my house will still be dry.

[jsmith45]

right. If there is a 100% chance of rain in half the forecast area, and a Zero percent chance in the other half, that is reported as a 50% chance of rain. But if you care about a particular spot, in theory you could be told the much more useful 0% or 100% number.

Obviously in reality it would never be quite that simple, but the point is that a spot forecast could be much more useful and accurate than an area forecast. (Of course, the more hours ahead the more you get into scenarios where for example just a slight drift in wind angle can give very different results on certain spots, while having more negligible impact averaged over an area.)

In any event we are not well set up for disseminating spot forecasts, but rather for disseminating area forecasts. In practice, as far as I have been able to determine, you can only easily get spot forecasts for airports.