It's during these times, when outdoor rides of any duration are difficult to do, that little bits of self doubts about physical preparation begin to creep in. I'm not sure what other people do to prepare for these events. For those who are "racing" endurance events, maybe they are doing the intervals on the trainer. I do my share of riding the rollers and watching some movies, but the best rides come from getting outside whenever I can. I always wonder just how much training is really necessary for these events. It's true that physical training is necessary. It would be darn right foolish not to train. But how much, and what kind of training is necessary? After a point, most of these long distance events are just a mental test. Listen to your body, and keep your mental resolve strong and the finish will take care of itself.
Winter rides, if you can manage them, are actually some of the most peaceful rides one can experience on a bike. There are even fewer cars on rural roads during this time of year. And there is certain bleak beauty that makes you feel very centered. Riding on snow and ice slows you down and takes away any sense of urgency. Long distance gravel rides like TransIowa are much the same (but warmer). If you can get rid of the "race urgency" and slow things down in your mind, the experience of simply riding can fill you with awe. And then doubt creeps back in and the re-centering process begins again.