Delayed Thunder lightning bolt

A stroke of lightning forming a 100-foot-long, 5-foot-wide line blasts out from you in a direction you choose. Each creature in the Line makes a Dexterity saving throw, taking 8d6 Lightning damage on a failed save or half as much damage on a successful one.  The lightning vanishes, but the arcane energy remains in its space, ready to release a shockwave when the spell ends. When the spell ends, each creature in the line makes a Constitution saving throw, taking Thunder damage equal to the total accumulated damage on a failed save or half as much damage on a successful one.

The spell’s base Thunder damage is 4d6, and the damage increases by 1d6 whenever your turn ends and the spell hasn’t ended.

Using a Higher-Level Spell Slot. The base lightning and thunder damage each increase by 1d6 for each spell slot level above 7.