A storm cloud appears at a point within range that you can see above yourself. It takes the shape of a Cylinder that is 10 feet tall with a 60-foot radius.
When you cast the spell, choose a point you can see under the cloud. A lightning bolt shoots from the cloud to that point. Each creature within 5 feet of that point makes a Dexterity saving throw, taking 3d10Lightning damage on a failed save or half as much damage on a successful one.
Until the spell ends, you can take a Magic action to call down lightning in that way again, targeting the same point or a different one.
If you're outdoors in a storm when you cast this spell, the spell gives you control over that storm instead of creating a new one. Under such conditions, the spell's damage increases by 1d10.
Using a Higher-Level Spell Slot
The damage increases by 1d10 for each spell slot level above 3.