It works in the cold fairly well since the heat of your wrist keeps the battery from freezing. In my skiing experience my phone often shuts down in the cold to protect the battery but the watch is always fine.

Apple specifically called out skiing and boarding in the keynote when they mentioned the altimeter. Which I'm really excited for!

Plus the current generations work fine in alpine conditions, from personal experience.

Quick calls and messages by Siri without taking my gloves off on the lift. Nice.