The giveaway is usually a door that drops crooked - one side hangs lower than the other, or the door won't budge past a foot off the floor and then binds. Sometimes you'll hear a loud snap and the door slams down on one side because the cable let go under tension. In this cold band, galvanized lift cables that flex all winter are the ones that give first, usually right at the drum or the bottom bracket, where the strand rubs the same spot every open-and-close cycle for years. If you see frayed wire poking out near the bottom roller bracket, stop using the door. A cable under tension that's about to fail can whip when it breaks, and it's not a repair to attempt yourself if the spring is still wound.