I find the rain affects the window cleaner more than the windows,Some custies dont like it but if im well away from home they have gotta be done,
One thing that is a problem in the rain (and wind) though is windows under trees or wall growing Ivy/plants, when water runs through the foliage and drips onto the glass it always leaves them dirty Suppose it would be the same trad but if you have a real 'grumbler' then its something to note.