Ball of Thunder

The air around your target crackles with static electricity and explodes in bright arcs of white-blue power.  Each creature in a 20 ft radius must make a Dexterity saving throw, taking 6d8 lighting damage and being knocked prone on a failed save, or dodging the arc on a successful save.  Once a bolt hits a creature, it spreads to another creature within 20 ft that has not yet been struck by Ball of Thunder.  Those creatures must make a Dexterity saving throw, taking 6d4 lighting damage on a failed save, or dodging the arc on a successful save.  The arcs then dissipate in a final burst of light.

At Higher Levels. When you cast this spell using a spell slot of 4th level or higher, the damage increases by 1d8 and 1d4 respectively for each slot level above 4th.