Extreme Cold

Whenever the temperature is at or below 30 degrees a creature exposed to the cold must succeed on a DC 20 Constitution saving throw every 15 minutes or gain one level of exhaustion.
Creatures with resistance or wearing cold weather gear (thick coats, gloves, and the like) and creatures naturally adapted to cold climates DC 10 Constution saving throw every hour.
Creatures with immunity to cold damage automatically succeed on the saving throw.