Niantic is giving players a limited amount of time to achieve a specific goal in Pokémon GO, and if they manage to do so, there will be a new event launched as a reward. The tweet below went out over the weekend from the game's official account letting players know of the challenge starting on March 5th.
Remember Trainers, If Rayquaza is defeated more than Kyogre and Groudon combined by 3/5, Pokémon that prefer windy weather will be more likely to hatch from Eggs starting 3/5. If not, Pokémon that prefer sunny or rainy weather will be more likely to hatch. https://t.co/AQY0qExLyp
— Pokémon GO (@PokemonGoApp) March 3, 2018
If the players manage to meet the goal (which the almost assuredly will) there will be an increased egg-hatching event for all dragon types, flying types, and psychic types once it's complete. Considering that Kyogre and Groudon and most likely going to vanish from the game again after their Raid Battles are up, this might be a good opportunity for some players to hit several birds with one stone, if they're coordinated enough and can pull together to make the event happen. But considering the fan's achievement rating is nearly 100% when it comes to timed challenges, this shouldn't be an issue.