It's not All Summer in a Day.
This was a story about explorers on Venus, who are separated from their base (possibly they're lost, possibly they suffered equipment failure, possibly they're just traveling from base to base) and are slowly being driven insane because it never stops raining.
The story is old enough that Venus' clouds were still believed to indicate a wet climate.
I can't remember much more detail than that. I have the impression that the narrator at one point either dreamed of or fantasized about walking into the destination base and being handed a very plush towel to dry off. I can't remember the central plot points - only the (very wet) setting. I would have read this in the late 1970's or early 1980's. I thought it might be an H. Beam Piper short story but I've been through his catalog and don't see any likely suspects.