Burning Ash Cloud

You create a 20-ft-radius sphere of ash at the target location that spreads around corners. The cloud's radius grows by 5 ft at the start of each of your turns. Its area is heavily obscured. When the spell ends, either because your concentration is broken or because you decide to end it, the cloud erupts with a dull roar into an explosion of ash and flame. Each creature inside the cloud must make a Dexterity saving throw. A creature takes fire damage equal to the total accumulated damage on a failed save, or half as much damage on a successful one.

The spell's base damage is 4d6. If at the end of your turn the cloud has not yet detonated, the damage increases by 1d6.

The fire damages objects in the area and ignites flammable objects that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the base damage increases by 1d6 for each slot level above 2nd.