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While a Pokémon with Cloud Nine is in play, the effects of weather are temporarily disabled. Fire- and Water-type moves are at normal power in sun and rain, SolarBeam has 120 base power and requires a charging turn, Blizzard and Thunder have normal accuracy, and Pokémon do not take damage from either sandstorm or hail. The game will report that the weather is still going, and the weather's effects will return when the Pokémon with Cloud Nine switches out.
Air Lock is identical.