Ashblast Cloak

Adorn a cloak of magically suspended ashes as a bonus action. Your Armour Class will increase by 3 for as long as you maintain concentration. You may disperse the cloak as an action, causing 2d6 + (casting modifier) fire damage to all entities within a 25ft sphere centered on your position. The sphere heavily obscures vision for everyone except you while you maintain concentration, causing a disadvantage on melee, ranged, and spell attacks. While inside the sphere, you may reform it back into the cloak as a bonus action. 

Casting at higher levels

4th level spell slot: 3d6 

5th level spell slot: 3d6, 35ft sphere

6th level spell slot: 4d6

7th level spell slot: 4d6, 45 ft sphere

No further Scaling.