Thunderbolt Sphere

A streak of light flashes from your open hand towards a direction  you choose within range then bursts with a thunderous roar into an explosion of lightning and thunder. Each creature in a 20-foot radius must make a Dexterity saving throw. A target takes 8d6 lightning thunder damage on a failed save, or half as much lightning damage and no thunder damage on a successful one. If a creature fails to make a saving throw they are also stunned until they are damaged by another attack or until their next turn. 

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d6 for each slot level above 4th.