Atmospheric Discharge

Massive amounts of electric energy converges at a single point in the sky, then shoots down as a powerful, guided blast of lightning. Choose a point at the ground within range, which is immediately struck by lightning from the clouds. The blast affects everything within 10 feet of the chosen spot, igniting flammable materials and objects. Creatures caught in the blast must make a Constitution saving throw or take 12d10 lightning damage, 12d10 thunder damage and be stunned until the end of their next turn and deafened for 1 minute. On a successful save, they are not stunned and take half as much damage.

The blast descends from the sky, so naturally it gets blocked by ceilings and other obstructions above the chosen spot. For optimal results, choose a spot open to the skies. If the bolt strikes a metal structure that connects to the ground, the lightning surges through it and causes no harm.