Eagle Napalm Strike

You deploy a torrent of flaming tar on a solid surface within range, up to 60 feet long, 20 wide. Each creature within its area must make a Dexterity saving throw. On a failed save, a creature takes 8d6 fire damage, or half as much damage on a successful save. When a creature starts it's turn in the napalm or enters it for the first time, it takes an additional 2d6 fire damage. 

The flames extinguish at the end of the start of your next turn.