This week is going to be a big one for Pokémon Go players.

Pokémon Go developer Niantic has announced two major additions to the game. First up is that 50 new Pokémon from the Ruby and Sapphire games will be joining Pokémon Go this week. These include Treecko, Torchic, and Mudkip. Niantic says that even more new monsters will appear in the coming weeks.

The other major new feature coming to Pokémon Go is real-world weather. This means that the in-game map will change with the weather in your area, complete with new visuals for weather types like rain, snow, and fog.

The weather changes will also impact the Pokémon that appear in the game. Certain Pokémon types will appear more frequently during certain weather types, like a Mudkip appearing more during a rainy time.

Additionally, certain weather attacks will be more effective during some weather conditions.