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Snow Warning

When this Pokémon is brought out, a permanent hail covers the battlefield. It can only be removed by bringing out a Pokémon with Drizzle, Drought, or Sand Stream, or by using Rain Dance, Sunny Day, or Sandstorm.

Smogon has an article on this topic.

Pokémon Type Tier Abilities HP Atk Def SpA SpD Spe BST
Abomasnow Grass / Ice BL Snow Warning 90 92 75 92 85 60 494
Snover Grass / Ice NU Snow Warning 60 62 50 62 60 40 334