Don't forget that the area most affected by cold weather is probably Barovia, which is the place where all new character arrives. Making cold weather harder to deal with would just make it harder for new character, the higher lvl char would not really be affected by that change since they can easily get gear to do the saving throw against cold.
This might seem right but the simple thing would be as stated make it like creeping doom. But to make it simple maybe instead of 1d6 make it 1d4 and just keep adding another d4 per tick to a max of Blah depending on temp. or if they are standing near a fire. without a fire and say below freezing the damage could cap out at about 20-28 damage on high end and 5-7 cold damage on the VERY low end and making the save just halfs the damage. that cloak will save you for at least a few rounds depending on luck. and you could last longer depending on gear. would give those thick fur armor reasons to be needed.
and before anyone says That's way to high of damage, clearly never climbed the mountain to Ice queen during the dead of winter and take 30-40 damage a tick with Protection from elements also in place.
And yes there is gear to help protect against cold, thick fur cloth and armor, most cloaks have 5 cold resist, the mountaineer cloak has 10 cold resist and now also has 5-15% fire vulnerability. I don't recall if comfortable leather boots gave 5-15% immunity. but if I recall it is 5% and that needs to be updated badly. cause that isn't helping anything at all. one would need to actually take 20 points of damage to have 5% remove 1 point of damage. But!! there is also feats which stack with items. and also spells. and fires reduce both damage and DC as well
I went to that mountain once and I'm aware that it that the cold damage is high, though, no early lvl character would go there and no one goes there if they're not well prepared, 20-28 dmg is too high because it'll instantly kill any new char.
Perhaps the dmg could be raised and I wouldn't be against it even though I think it's not necessary, but if its to high it mean no new character with little gold won't be able to go outside during winter, or won't be able to for a long time.
When I play a new character, I'd hate having to buy a tons of gear to protect myself against cold. I've never been very good at making gold and I surely am not the only one. Yes it would be more realistic, but there is no point in making something super realistic if it hurts the gameplay. I don't like making new char because it's not always easy, some player even leave after a few days/weeks because they have too much difficulty starting their char, making the starting area harder to survive I think wouldn't be a wise move in my opinion.