Caspian's Storm Whip

You create an whip made from a storm that lasts for the duration,  that deals either lightning or thunder damage, you choose when you cast the spell. When you cast the spell, you can make a melee spell attack against a creature within 15 feet of yourself. On a hit, the target takes damage to equal to 5d8 + your spell-casting ability modifier according to the damage type you chose.

At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, the damage increases by 1d8 for every two slot levels above 5th.