Two mathematicians have for the first time created a computer simulation that generates realistic three-dimensional snowflakes, although even they are not sure how it works.

"We know surprisingly little about how ice crystals grow," says California Institute of Technology physicist Professor Ken Libbrecht, who is considered a leading expert in snow crystal physics.

Mathematicians Professor Janko Gravner of the University of California, Davis and Professor David Griffeath of the University of Wisconsin-Madison have avoided the old approach of virtually building the snow crystals molecule-by-molecule.

Instead, they use virtual 3-D cells much larger than water molecules, which behave according to the same physics thought to control crystal growth.

He and Griffeath created their virtual cells, called cellular automata, to be one cubic micron in size.

At that scale the cells, about the size of a speck of dust, mimic the physics of water vapour and crystalline growth.