the snow in Hogan's bothered me too. Schultz picked flowers in Klink's yard, the prisoners plant flowers to disguise a dirt trail, they go out to pick grapes...
I looked it up a couple of years ago, the constant winter was so the episodes had continuity. Rerun older shows were picking up in popularity, and mixed up they were always in order, so to speak.
After the first season, they used salt to mimic snow.