Comment by GeoffKnauth

From talking with meteorologists, it seems forecasting actual rain is not very hard if you have enough current data on the state of the atmosphere. What can be difficult is mistiness that is just on the borderline between falling droplets and moisture just hanging in the air. Differences can be extremely local in nature. [I'm not a meteorologist, I program computers, but I'm a pilot so I have a pilot's appreciation of and contact with weather.]