Delayed Strike Lightning Bolt

You create a faintly glowing ball of lightning that coalesces between your palms for the spell's duration. When the spell ends, either because your concentration is broken, or you decide to end it, a stroke of lightning forming a line 100 feet long and 5 feet wide blasts out from you in a direction you choose. Each creature in the line must make a Dexterity saving throw. A creature takes lightning damage equal to the total accumulated damage on a failed save, or half as much damage on a successful one. The spell's base damage is 12d6. If at the end of your turn the bolt has not been fired, the damage increases by 1d6. You can attempt to conceal the ball by making a sleight of hand (Dexterity) check against an enemy's insight (Wisdom) check.