Thunderhead

You summon a roiling thundercloud, which flickers with lightning before emitting a series of thunderous rumbles. The thundercloud takes the shape of a 30-foot radius, 30-foot high cylinder, centered on a point you choose within range.
When the cloud appears, each creature in it must make a Dexterity saving throw or take 3d6 lightning damage, or half as much on a successful save. As an action on each of your turns, you can cause lightning to flash through the cloud again. Any creature that ends it's turn in the cloud must make a Constitution saving throw or take 2d10 thunder damage, or half as much on a successful save. 
As a bonus action while you are within 120 feet of the cloud, you can move it up to 30 feet.
At Higher Levels. When you cast this spell with a spell slot of 6th level or higher, the lightning damage increases by 1d6 for each spell level above 5th.