Today starts the Articuno Day event.
All tier 5 raids will be taken over by Articuno's. There is no indication of how many shinies will be available during the event time but there will be some. Keep in mind some area raids may not have any shinies at all.
You will be able to pick up 5 five free passes during the 3 hour event but can only hold one pass at a time.
Articunos are weak to Rock pokes so Tyranitars, Golems and Omastars are highly recommended when battling the legendary birds but also Raikou, Blaziken and Moltres are equally helpful.
Also keep in mind the time zones for your region on when the event will start/end below:
The Asia-Pacific region: 12:00 p.m. to 3:00 p.m. JST (GMT +9)
Europe, the Middle East, Africa, and India: 9:00 a.m.to 12:00 p.m. UTC (GMT +0)
The Americas and Greenland: 11:00 a.m. to 2:00 p.m. PT (GMT -8)
And don't forget Squirtle Community day tomorrow starting at 11am PST!
Feel free to add me to your friends list in Pokémon GO! My Trainer Code is 2474 3982 7220!