Dragon King's Cataclysmic Lightning Storm

The clouds darken and the sky rumbles as the heavens let out a roaring boom, primordial lightning strikes the ground at four different points you can see within range. Each creature in a 40-foot-radius sphere centered on each point you choose must make a Dexterity saving throw. The sphere spreads around corners. A creature takes 40d6 Lightning damage on a failed save, or half as much damage on a successful one. 

The spell damages objects in the area and ignites flammable objects that aren't being worn or carried.