I live in North Texas and the winters here are usually mild, but this past winter it actually got pretty cold along with some decent snow.
Our dogs are small (5.5 lbs & 6 lbs) and before they went outside, I made sure they had their sweaters on. If it was
really cold, I put their little jackets on over their sweaters. Plus, I only let them outside for about 10 minutes maximum at a time.
I think it depends on your dog, too. Our little Coco
loved the snow and jumped around in it like a little rabbit, but Gracie didn't want anything to do with it.
To me, it's very important to keep them warm because of their size (small animals lose body heat more quickly than large animals). If I'm in doubt about it being too cold or not, I err on the side of caution and just keep them inside and they can take care of dirty business on their pee pads.
If it's cool out, I would definitely recommend a little sweater, limit time outside, and maybe even leave the sweater on for a little while after he comes in until he can get re-acclimated. I don't think he'll overheat !!!
Good luck !!