Niantic have announced the details for the January 2020 Pokémon GO Community Day which takes place on January 19th, 2020 at 11:00 AM until 2:00 PM EST in the Northern Hemisphere and 3:00 PM until 6:00 PM in the Southern Hemisphere. The featured Pokémon for this day is Piplup. Piplup will appear in the wild more frequently for three hours that day. If you evolve Prinplup into Empoleon, it will know the move, Hydro Cannon. The 1/4 Egg Hatch Distance and 3-hour Lures bonuses will also be available that day.

Source: https://pokemongolive.com/events/community-day/