You touch one nonmagical weapon and imbue it with frost. For the duration, the weapon and any ammunition it fires are coated in a thin, biting layer of ice, and any damage the weapon deals is cold damage instead of its normal damage type. If a hit with the weapon is a critical hit, the weapon deals an extra 1d4 cold damage, and the spell ends.    The cold damage from a critical hit increases by 1d4 when you reach 5th level (2d4), 11th level (3d4), and 17th level (4d4).