Thrym’s Howl
Eldritch Storm
These bone-chilling blizzards drive a wall of wind and snow like a living glacier. The storm projects extreme cold (see the “Dungeon Master’s Guide”). Due to the howling wind and dense blue-white ice particles, the area in the storm is heavily obscured, and ranged attack rolls and Wisdom (Perception) checks made within it have disadvantage.
Any creature exposed to the storm at the start of its turn takes 2d6 cold damage and can’t regain hit points until it spends at least 1 hour in a warm environment. A creature that dies in the storm freezes solid. Creatures that are immune to cold damage are immune to the effects of the storm and can see normally within it.
Thrym’s howl typically lasts 2d10 hours.
Source: Tasha’s Cauldron of Everything p. 163