Delayed Blast Thunderwave

The air around you crackles with energy as you gather energy for a blast of thunderous power. When the spell ends, either because your concentration is broken or because you decide to end it, you release the stored energy in a wave of destruction.  Each creature in a 15-foot cube originating from you must make a Constitution 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 8d8. If at the end of your turn the energy has not been released, the damage increases by 1d8.

In addition, unsecured objects that are completely within the area of effect are automatically pushed 10 feet away from you by the spell's effect, and the spell emits a thunderous boom audible out to 300 feet.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the base increases by 1d8 for each slot level above 5th.