Chances are, the outside dog is already built for seasonal changes. Fur gets thicker, for instance. That doesn't mean you should rest and let nature take its course. There are still things you can and should do for your outdoor dog in the winter.
Shelter. Dog houses are nice, cozy places where the dog can rest in relative warmth. You can also do a lot of good by providing a larger roaming space if possible. Living in the country, we cornered off a section of our barn for our large dog. A heating lamp was then hung from a rafter and a hole was cut into the barn wall to give him access to and from his indoor refuge. Not everyone can go this far, but even a couple hours or so a day in an enclosed porch can give him a warm place to exercise.
Food and water. Check your dog's food and water daily. He should always have enough food. Water tends to freeze if left to stagnate in the cold, and hydration is important for health. Heated dog bowls are available if you are strapped for ideas. Keeping the water constantly circulating, has also worked for my family.
Company. It's cold out there, and you may not want to spend as much time with your outdoor dog. Do it anyway when the chance presents itself. A well trained dog will be happy to see you, and can stay that way if you keep working with him.
Next: Part 2: The Inside Dog
(Once again, I decide to count on personal experience to fill up another pet care article. Living in Michigan for 21 years was quite an experience. Having the variety of dogs and circumstances that we did often meant using several solutions on different pets at the same time. The usual comments apply: this is not all-inclusive nor am I an expert in these matters. I'm just a webmaster who has owned more than a few pets and is sharing ideas.)