I have had active dogs for the past 20-plus years, and they love running through the deep snow where I live, but dogs in different locales have different needs come wintertime. In general, smaller and short-coated dogs need to worry more about a warmth, dogs walked during hunting season or after work in the earlier darkness need to worry about visibility and many dogs have to worry about their paws.
Some dogs can get away with a thin fleece sweater, but if your dog is especially sensitive to the cold or is going to be spending a lot of time outdoors (such as hiking or skiing in winter), the top of the line choice is the Powder Hound by Ruffwear. The hybrid construction combines synthetic insulation that packs in warmth and will still work even if it gets wet with active stretch fabrics to allow unlimited freedom of movement. This is important because this model completely covers the dog’s underbelly and the tops of its front legs, which most coats do not, and this prevents uncomfortable snow buildup that often occurs on the chest and underarms. It is lined with cozy fleece on the inside and comes in three colors and sizes, for dogs from XXS to XL.
