Cowl of the Tempest

You electrify the air around you, giving yourself the aura of the tempest. At the end of your turn, all creatures within 10 feet of you must make a Dexterity saving throw or take 2d10 lightning damage on a failed save, or half as much on a successful save. If a creature moves into your aura they must also make the saving throw. 

At Higher Levels: When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d10 for each slot level above 2nd.