Turnouts are generally water proof, but make sure it says that and not just water resistant.I was just also wondering do most of them come water proof, and if not how do I do that? (Like who would waterproof blankets *Like what sillybunny was saying*)
I know it gets mighty cold in MN, but also consider the weight (light/medium/heavy) carefully. Assuming your horse is not clipped, with any blanket you'll need to make sure you take it off whenever it's 'warm' since horses can quickly become over heated with blankets. For horses with a good winter coat, many folks will use water proof turnout sheets instead of blankets to protect from the water and wind, which chills them the most, and they can generally be left on all the time.