Elemental weakness

The next time you hit a creature with a melee weapon attack during the spell’s duration, your weapon exposes the creature to the elements. You deal 1d6 random elemental damage as shown below. for the next minute or until you break Concentration the creature is vulnerable to all elemental damage that it has not been damaged by the last and gains resistance to the last elemental damage taken.

Elemental damage: Roll 1d6 to determine damage before rolling damage

1-2: Cold  3-4 Fire  5-6 :Lightning 

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the initial extra damage dealt by the attack increases by 1d6 for each slot.