Tempest

The caster unleashes a fierce lightning storm that deals constant electricity damage to anyone in the targeted area. 
Each creature in a 40-foot-radius Sphere centered on that point makes a Dexterity saving throw, taking 6d6 Lightning damage on a failed save or half as much damage on a successful one. On subsequent turns for the duration of the spell, each creature within the affected area makes another Dexterity saving throw, taking an additional 2D6 Lightning Damage.
The affected area becomes Difficult Terrain and is considered Half Cover.

Using a Higher-Level Spell Slot. The damage increases by 1d6 for each spell slot level above 7.