AZ-0003 · Instruments
Snowflake Generator
Crystallus sexangulus
Grow a realistic ice crystal from the temperature and humidity of a cloud, or draw your own snowflake, then save it as an image and share a link.
Snowflake Generator
Notes on snow crystals, Vermont
A snow crystal grows from a speck of ice as water vapour freezes onto it, and the weather decides its shape. This one is grown by a simulation of that process on a hexagonal grid: temperature and humidity set how the crystal takes up vapour, so the same rules give plates, sectored plates or branching dendrites. Change the weather while it grows, and the crystal keeps the record of it, like a real flake falling through layers of cloud. All six arms stay alike, because they all met the same weather.
How a snowflake forms
A speck, then a prism
A snowflake starts in a cloud, where water vapour freezes onto a speck of dust or pollen. The first crystal is a tiny six-sided prism of ice.
Why six sides
Water molecules lock into a hexagonal lattice as they freeze, and the crystal's shape follows that lattice.
Why it grows arms
The corners of the prism stick out into the vapour and catch it fastest, so they outgrow the flat faces and sprout arms. Side branches grow from the arms the same way.
What sets the shape
Temperature and humidity. Moist air grows branches; dry air keeps the crystal simple. Try −15 °C with the humidity slider high, and the generator grows stellar dendrites.
| Air | Real snow grows | This generator draws |
|---|---|---|
| about −2 °C | thin plates | sectored plates |
| about −5 °C | columns and needles | thick plates |
| about −10 °C | plates again, often sectored | sectored plates |
| about −15 °C | stars and ferns (dendrites) | stellar dendrites |
The generator's model is flat, so it cannot draw columns or needles. Around −5 °C it grows thick plates instead.
Why the six arms match
All six grow at the same time in the same air, so they meet the same conditions together.
Why no two are alike
Each flake falls its own path through changing air. Change the weather while the crystal grows here and you are imitating that history.
Who worked it out
Wilson Bentley photographed snow crystals in Jericho, Vermont, from 1885. In the 1930s Ukichiro Nakaya grew crystals in his laboratory and charted how they depend on temperature and humidity. Kenneth Libbrecht continues the work today.
Sources: Libbrecht, snowcrystals.com (morphology diagram and science pages); Libbrecht, “The physics of snow crystals”, Reports on Progress in Physics 68 (2005); Bentley and Humphreys, Snow Crystals (1931).
Saving and sharing
Save as image downloads the crystal as a PNG on a dark field. Copy link gives you an address that holds the seed and the weather, including any change you made while it grew, so whoever opens it sees exactly the crystal you made, on any device.
Snowflake Generator
Crystallus sexangulus
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Grow a realistic ice crystal from the temperature and humidity of a cloud, or draw your own snowflake, then save it as an image and share a link.
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