Thundaga (Thunder III)

You launch an unstable sphere of lightning aspected aether at a target of your choice you can see within range. Make a ranged spell attack. On a hit, the sphere deals 4d8 lightning damage. The sphere then explodes in a 10ft. radius sphere. All creatures in range must succeed on a Dexterity saving throw or take 4d8 lightning damage, and half as much on a success.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage dealt by the explosion increases by 1d8 for each slot level above 3rd.