Giant Snowflakes

Since at least the 19th century, people have periodically claimed to see giant snowflakes falling from the sky — big ones the size of saucers and plates or even larger, their edges turned up, their heaviness making them descend faster than small flakes.

But the evidence of their existence was always sketchy. Now, theorists, weather historians and field observers are concluding that most of the reports are true and that unusually large snowflakes two to six inches wide and perhaps wider fall regularly around the globe.

Guinness World Records lists the largest snowflakes as having fallen during a storm in January 1887 at Fort Keogh, in Montana. A rancher nearby, the book says, called them “larger than milk pans” and measured one at 15 inches wide. But no corroborating evidence supports the claim.

Snow crystals, despite their legendary diversity, come in a relatively small number of general shapes, including prisms, columns, stars, cups, plates, bullets and needles. Technically, the big crystals are known as dendrites, from the Greek word for tree, because their arms are quite elaborate, like branches thick with leaves or flower stems rich in petals. Dendrites are the largest snow crystals.

Scientists have found that dendrites have a tendency to join together faster than their simpler relatives. Their complicated arms, it appears, more easily form bonds.