The address of the page keeps the crystal's weather, to share it.
A letter from the sky
A snowflake starts as a speck of dust in a cloud, colder than freezing and full of water vapor. Vapor freezes onto it molecule by molecule, and because ice is hexagonal, the crystal grows six-fold. Its corners reach farther into the moist air than its faces, so they grow faster and sprout into arms, and the arms sprout branches. All six arms live through the same weather on the way down, so they grow alike, but no two snowflakes take the same path.
Ukichiro Nakaya, who grew the first artificial snow crystals in 1936, showed that their shape depends on just two things: temperature, which decides between plates and columns, and how humid the air is, which decides how branched they get. He called snowflakes "letters from the sky": reading one tells you the weather it fell through.
This page grows them with Clifford Reiter's model (2005), a grid of hexagonal cells that each hold some water. Ice cells, and the cells that touch them, keep their water and gain a little from the cold (the frost, γ); the others share theirs with their neighbors (the diffusion, α). A cell freezes when its water reaches 1, and the air far away holds the background humidity, β. Dry air gives stars of thin, ferny arms; humid air gives plates and lace. Tick Drift to let the weather change while it grows, as it does for a real snowflake.