Atomic Blast Fireball

A large roaring ball of fire erupts within your hands, growing in size for every round not cast. When this spell ends willingly, chose a point within range. The ball from your hands is thrown forward, and each creature in a 60-foot-radius sphere centered on that point 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. If the spells concentration is broken unwillingly before you cast it, the target is centered on yourself and the spell is immediately cast.

The spell's base damage is 20d6. If at the end of your turn the ball has not yet detonated, the damage increases by 4d6. If you successfully release the spell after 5 rounds of concentrating on it (the maximum amount of time that you can concentrate on it), the damage dealt is automatically max.

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