So it's like -20 degrees fahrenheit outside the house I'm staying at and the wind chill is between -40 and -55 degrees. The wind itself has been constant since yesterday, blowing snow across roads, reducing visibility. And there's frost on the inside of some of the window sills.
If you want to have a taste of what's it like inside G2: The Glacier Rift of the Frost Giant Jarl, then by all means comes travel to the Midwest before things start warming up tomorrow.
All of this has gotten me to realize that I've never run a campaign featuring extreme cold. The closed I came was about three years ago, when the PCs had to ascend a mountain. The brought along warm clothes--and they weren't even going to the top. That took care of that.
I've been skimming through various rules for characters enduring cold weather in the AD&D Wilderness Survival Guide and the 3.5e Frostburn. It seems like the rules are more complicated than the need to be.
I'd just see the rules as guidelines and use DM fiat. If you don't bundle up--including extremities--you're going to take some damage.
Yet how else do you quantify being in extreme cold?
Since I've never run a campaign featuring the extreme cold I'm facing here in the midwest, I'll just say it's best that your characters should just stay home and wait until it warms up.