It would halve the negative effects of weather, increase the character’s tolerance to Cold/Heat and reduce the penalties to natural bad weather (which means no effect on acid rain).
Discuss.
Would it protect from the Wet bad though, or only heat-related things?
While not a bad idea, I would worry about the indirect implications. Not having to worry about temperature so much would be nice, but as soon as you can basically wear half the gear, that immediately translates to wearing more armor with less encumbrance. And since encumbrance is the great balancing pivot of gear-vs-combat, I can see it translating to being indirectly overpowered.
I think a trait which reduces the mood consequences of being wet/cold would be better. That way you would still need to worry about cold extremities reducing combat ability/skill usage, cold waking you up, and frostbite doing damage. It just wouldn’t depress the hell out of you to be cold and wet which pretty much is going to happen once in a while regardless, and would make crafting in the cold and rain easier.