We were out last weekend at a low of 8-9F. Hypothermia would be on the forefront eh, but years ago I spent 2 weeks boardsailing in Aruba. Before they let us go out we had to undergo a training class on the dangers. They told us of what happens if you fall off your board and stand or lang on a sea urchin but they also told us that Florida has the highest cases of hypothermia in the country. True? I didn't argue but the point is that it can happen when and where you least expect it.
Probably counterintuitive, but drinking cold water when its cold outside is exactly what I did last weekend and chased it with cashews and chocolate/cherry MMs
The ones I always see on the trail are Scouts with poor leaders hiking in cotton (in our eastern woodlands) in the rain and in temps between 38-52F.