What makes some snowflakes so large?

Memes from a more Civilized Age… on Instagram: "The world's largest snowflake ever recorded was 15 inches wide and 8 inches thick. It was observed in Fort Keogh, Montana, in 1887. This massive snowflake was so large that it was described as being "like a dinner plate" by the observer. While the official record is disputed by some, the sheer size of this snowflake is still a testament to the incredible power of nature. Imagine the beauty of such a large, intricate snowflake falling from the sky!