A storm cloud appears in the shape of a cylinder that is 10 feet tall with a 60-foot radius, centered on a point you can see 100 feet directly above you. The spell fails if you can't see a point in the air where the storm cloud could appear (for example, if you are in a room that can't accommodate the cloud).

When cast and at the start of each of your subsequent turns a bolt a lightning streaks from the sky to strike one randomly determined creature within range, unless you use a bonus action to prevent it from doing so. The creature must make a Dexterity saving throw, taking 2d10 lightning on a failed save or half as much on a success. This effect continues for one minute or until you take an action to end the spell.

If you are outdoors in stormy conditions when you cast this spell, the spell takes control over the existing storm instead of creating a new one. Under such conditions, the spell's damage increases by 1d10.

At Higher Levels. When this spell is cast using a spell slot of 2nd level or higher, its damage increases by 1d10 for each slot level above 1st.