Fran, if Homer is not done with his series of shots, I would be careful taking him outside. I remember when Mason was 10 weeks and only had 2 sets of shots my vet telling me that he shouldn't be out where he can sniff other dog's pee/poop because he can catch diseases. So I would suggest that you either wait until Homer gets all his shots, or take him out for very short walks and keep him on a sidewalk.
In terms of weather, I don't let Mason out when there is snow outside. In the past I have let him walk in the snow and his bottom paw turned so red I felt aweful. ALso he has gotten sick this past winter so I am very cautious of letting him out in the cold. But 39degrees F seems fine. I would put a sweater on him though.
Oh, and StewiesMom, I am a WOLVERINE, you better watch out
