Arcs of Keranos

You invoke the power of Keranos, the God of Storms. Arcs of Lightning erupt from you and batter all creatures within 15 feet of you. Each creature in that area must make a Dexterity saving throw. On a failed save, a target takes 2d8 Lightning damage and can’t take reactions until its next turn. On a successful save, the creature takes half damage, but suffers no other effect. 

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d8 for each slot level above 2nd.