I’m going to be the odd one out here. I don’t see why winter training should be very much different to the rest of the year: go hard all the time! BUT if your miles/frequency of riding falls off because of the weather and road conditions then you will lose fitness and you’ll do yourself a mischief if you overdo it. So, I think the answer is DON’T push it until you’re properly warmed up and be realistic about the distances you are doing. But taking it easy and plodding along? Not ideal but ANY miles are a good thing!