Acid Rain

You conjure up a cloud filled with acid at a point you can see within range. The cloud has a 30ft radius circle but you can choose to shape it as a 10ft wide and 20ft long rectangle instead. It instantly starts to pour down acid rain for as long as you keep concentration.

Any creature starting their turn in that area or entering the area for the first time needs to make a Constitution saving throw. On a failed save the creature takes 10d4 acid damage, or half on a successful one. Any creatures injured by this acid no matter if they save or not, will take an additional 2d4 acid damage at the end of every turn until they spend an action to get the acid off. This effect remains even if the spell has ended. For every minute spent taking this acid damage it will lower the AC of any non-magical armor or shield that the creature is wearing or wielding, by 1 until the armor reaches 0 and then is evaporated. 

While a creature is standing in the rain they have disadvantage on all attack rolls and are considered blinded.

At Higher Levels. When you cast this spell using a spellslot of 4th level or higher, the initial damage increases by 2d4 for each slot level above 3rd.