Black Lightning Strike

A black mote is shot high into the air from your hand, you point at a area and a storm of black lightning strikes are shot down. Each creature in a 20-foot-radius sphere centered on that point makes a Dexterity saving throw, taking 8d8 lightning damage and become paralyzed on a failed save or half as much damage and not paralyzed on a successful one. If the spell is used outside or in an open air area, the damage increases to 10d8 Any creature who becomes paralyzed as a result of this spell can attempt to break the condition at the end of their turn by making another Dexterity saving throw. The ground in the radius of this spell becomes rough terrain due to the lightnings impact into the ground. 

Using a Higher-Level Spell Slot. The damage increases by 1d8 for each spell slot level above 5.