Whirl, O Flame

You create a spiraling stream of fire in a line 30 feet long and 5 feet wide. Each creature in the line must make a Dexterity saving throw. A creature takes 4d8 fire damage on a failed save, or half as much on a successful one.
At Higher Levels.
When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8 for each slot level above 2nd.