British hardman Andy Kirkpatrick has not only climbed El Capitan more than 30 times, he’s also climbed remote big wall expedition routes in some extremely cold and harsh conditions all over the world. He knows a lot about staying warm and coming back in one piece. Most of the tips below are from his excellent big wall book, “Higher Education”, definitely recommended reading if you want to climb the big stuff.
This is hopefully painfully obvious, but always bring a rain fly for your portaledge, no matter how cheerful the forecast.
Always try to stay dry, or at least as dry as you can. “You will always be wet in a storm, but there’s a difference between damp and warm, and soaking and shivering.”
If you’re already warm and dry, do everything you can to stay that way. That means, don’t leave your nice dry portaledge to go out in the rain and fix a pitch.
If you’re leading and starting to get wet, really think through whether you should be pushing on in the storm, or retreating back to your dry ledge.
Even in summer conditions, bring clothing like you’re on a winter alpine route. When you’re hauling 100 kg of gear, and you’ve got a 170 liter haul bag, bringing some extra warm gear that you already own is really not that big a deal.
What kind of warm gear? Synthetic sleeping bag, (never down) with a minimum rating of 20 Fahrenheit. Long underwear, top and bottom, at least one pair of warm socks for sleeping, fleece top, Das Parka type synthetic belay jacket, balaclava, gloves.
Use a bivy sack over your sleeping bag, in addition to the fly on your ledge.
Do everything you can to keep your sleeping bag dry. It's your largest piece of warm “clothing” and last line of defense. If all of your clothes are truly wet, consider wrapping the sleeping bag inside of a bivy sack over you like a blanket rather than you being inside the bag.
Avoid getting into a dry sleeping bag with wet clothes. Change into dry clothes first, or take off all your clothes and get into your bag.
Have a small sponge to mop up water and condensation.
If you know a storm is coming in, make sure you have everything you need in or accessible to your ledge, so you don’t have to go out in the storm and burrow through your haul bag.