What I really pay attention to is cold hands. When fingers go numb, trigger control and basic gun handling can quickly go downhill, so I slow things down and make sure they’re using gloves that are practical, not those bulky ski mitts.
Staying safe in the winter is mostly about keeping people comfortable enough to pay attention. Cold hands make it hard to pull the trigger smoothly, so I tell people to take breaks a lot and do simple drills instead of long, complicated ones.