Observations
"If there is such a bad spacial resoltion of observation stations how do you get good values for locations in between? Can you merely interpolate?"
"Yes, you found exactly the weakness. A mere interpolation will in most cases not be correct. You must take into account orography and possibly other relevant data sources. So parameters like radar and satellites but also the model analyses have to be combined to get an optimum analysis and we think that we can get close to the (not known) reality. But you never will arrive at a complete correct analysis."
"The next set of data is Radar. Follow
this link
to learn more!"