Blizzard

You cause a torrent of icy wind to sweep across the battlefield, manifesting as a blizzard. The blizzard appears in a 50 ft. Cube within range. When a creature enters the area for the first time on its turn, or starts its turn in the area, it must make a Constitution saving throw. On a failure, a creature takes 8d8 Cold damage, and their Speed is halved for the duration. On a success, a creature takes half as much damage only. If a creature within the blizzard fails its saving throw while it has its Speed reduced in this way, its speed is reduced to 0.

Creatures that have their Speed reduced by this spell can repeat their saving throws at the end of each of their turns, ending the effect on themselves on a success. Failing this saving throw does not reduce their Speed to 0. As a Bonus Action on each of your subsequent turns, you can move the blizzard up to 30 ft. in any direction.