Thunder/Lightning Sphere

A sphere of thunder/lightning appears around the caster covering an area 15ft radius. The sphere is opaque and lasts for the duration or until the caster loses his concentration. When you cast this spell, designate any number of creatures you can see within 60ft of you to be unaffected by it. A creature  that enters the spell’s area takes 4d6 thunder damage and makes a STR saving throw with DC equal to the caster + the spell level. If he fails he is pushed 10ft away from you in a straight line. When you cast the spell and as an action each round for the duration, you can channel some of the sphere’s lightning energy to create a lightning bolt which you hurl to a creature or object within range which you can see. (A maximum of three lightning bolts can be created like this and once all three lightning bolts are used the spell ends. For every lightning bolt used, the sphere’s radius decreases by 5ft) Make a ranged spell attack against the target. On a hit, the target takes 4d10 lightning damage and makes a STR saving throw with DC equal to the caster + the spell level.If he fails the throw he is prone.

At higher levels. When you cast this spell using a spell slot of 4th level or higher, the sphere radius increases by 5 feet and the spell creates one additional lightning bolt for each slot level above 4th. When cast at 8th level the damage of the lightning bolts increases by 2D10.