Ryan Jordan’s advice:

And so, if you’re heading out into winter crap, which is about the only term that describes “temperatures near freezing with sustained heavy snow and rain and no opportunity to dry gear”, follow these rules:

1. Down won’t work. Don’t even try to make it work. No waterproof-breathable fabric bivy sack or tent will help. No super breathable system (think: tarp, no bivy) will help. At these temperatures, the dew point will be inside the bag and any moisture in your shelter (bivy, tent, tarp, snow cave, it doesn’t matter) will condense on the outer fabric. You’ll pack your wet bag into a stuff sack in the morning and enjoy the beginning of an absolutely awful night when you unpack it that evening.

2. Synthetics won’t work either. But they at least will allow you to spend an extra night or two.

He found that synthetic insulation lost tons o’ loft in only a couple nights outdoors in snowy, hovering-near-freezing weather. Goes to show that the tiniest variances in temperature can trip you up when you’re out in the cold. All the more reason to “camp” in a cabin with a nice warm fire.