A swirling cloud of smoke shot through with white-hot embers appears in a 20-foot-radius sphere centered on a point within range. The cloud spreads around corners and is heavily obscured. It lasts for the duration or until a wind of moderate or greater speed (at least 10 miles per hour) disperses it.   When the cloud appears, each creature in it must make a Dexterity saving throw. A creature takes 10d8 fire damage on a failed save, or half as much damage on a successful one. A creature must also make this saving throw when it enters the spell's area for the first time on a turn or ends its turn there.   The cloud moves 10 feet directly away from you in a direction that you choose at the start of each of your turns.