Does mid-air refueling have very hard constraints on weather? I'm guessing mid-air refueling has constraints on windspeed and wind direction, visibility, and precipitation. I may have missed some, but those alone make me feel like mid-air refueling can't be done most of the time (?)

About wind direction though, I guess you could just fly in the "right direction", but then this would also have constraints because the "right" direction could lead away from your ultimate destination.

(also, is there a mid-air refueling tag I couldn't find?)
The receiver has to have visual contact with the tanker to complete the rejoin, so finding a clear block of airspace (i.e. not IMC) is necessary. Beyond that, none of the factors mentioned really matter much.  Turbulence can make refueling more difficult, although it's often possible to find an altitude with a decent ride.

Mostly, AR can be done; the times when it can't are much more the exception.