The Largest Snowflake Ever Recorded Was 38 Centimeters Wide

While we often imagine snowflakes as tiny, perfect crystals, the most colossal examples are actually messy conglomerates. These giants, known as aggregate snowflakes, form under a very specific set of atmospheric conditions. The air temperature needs to be just slightly above freezing, causing the outer surfaces of individual snow crystals to become moist and sticky. In calm, windless air, these tacky crystals gently collide and adhere to one another as they fall. Instead of a single, six-sided dendrite, the result is a massive, fragile lattice of many smaller crystals fused together.

This is precisely what happened in the skies above Fort Keogh, Montana, on a winter day in 1887. An army officer at the post (Review) reported seeing flakes "larger than milk pans," with one measuring an astonishing 38 centimeters (15 inches) across and 20 centimeters (8 inches) thick. While we lack photographic proof from that era, the report remains the official world record. It stands as a testament to how, with the right combination of warmth, moisture, and stillness, countless tiny ice crystals can unite to create something truly monumental.