I think a thunderstorm would be cool. Kinda like rain but with a chance of damaging a non-Electric type with lightning. Steel types would get hit more often. And the thunderstorm boosts the power of Electric type moves.
But that wouldn't hinder Water very much, would it?
"Definition: 'Love' is making a shot to the knees of a target 120 kilometers away using an Aratech sniper rifle with a tri-light scope." -HK-47