Google's banner on Jan 28 celebrated the 125th anniversary of the largest observed snowflake. Source: Google
Anyone who has made snowflakes by cutting up folded pieces of paper, but has never actually seen them drift down from the sky, probably has a distorted view of their size. Most of them aren't that big, typically smaller than a CD, but there have been claims of snowflakes reaching the size of Frisbees.
Google paid tribute Jan. 28 to the world's largest observed snowflake on the 125th anniversary of its supposed sighting with a pastoral wintry banner, depicting a massive snowflake 10 times the size of a perplexed cow off to the side. The actual snowflake, witnessed by a rancher in Fort Keogh, Montana, in 1887, was said to be 15 inches in diameter--closer to a cow's head than a flying saucer, but that really wouldn't make for a very interesting banner.
Most snowflakes don't get very big due to their delicate structure, and can easily break down from strong winds or insufficient cold weather. The colder the temperature, the larger the snowflake can get and the more intricate its patterns become.
Perhaps the snowflakes in Antarctica are bigger, with elegant crystalline branches and dendrites, but the scientists there haven't seemed to find anything. Maybe the penguins know.