Thundering Lash

A arc of lightning forming a line 30 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 6d6 lightning damage on a failed save, or half as much damage on a successful one. After a round a thundering echo takes place occuring 30 feet long and 15 ft wide in the same dirrection as the lighting. Each creature in the line must make a Dexterity saving throw. A creature takes 4d4 lightning damage on a failed save, or half as much damage on a successful one
The lightning ignites flammable objects in the area that aren't being worn or carried.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the damage increases by 1d6 & 1d4 for each slot level above 4th.