https://www.gamespot.com/articles/pokemon-go-legendary-articuno-returns-this-week/1100-6460195/

The Pokemon Go Summer Tour made its first stop this past weekend with a special Safari Zone event in Dortmund, Germany. During the event, players around the world had a chance to participate in Global Challenges, and developer Niantic has revealed the reward for their efforts: another opportunity to catch the Legendary bird Articuno.

This Saturday, July 7, Articuno will return to Raid Battles for a limited time. The Legendary Ice-type will only be available for three hours, but Niantic has confirmed it will be the only Tier 5 Raid Boss going on around the world during that window of time, temporarily replacing the game's current Legendary, Regice.