SKYWRITING

Every crystal here is grown live on your GPU by the Gravner–Griffeath model (Physica D 237, 2008) — vapor diffuses, freezes onto the edge, and the attachment rules prefer facets or throw branches depending on where in the diagram you are. The horizontal axis is temperature, the vertical axis is how much more vapor the air holds than ice can bear (the Nakaya diagram). Your finger is the weather.

Honesty: the mapping from (temperature, excess vapor) to the model's parameters is calibrated by hand to reproduce the classic regimes, then never touched; the physics decides everything after that. The Sapporo preset follows the real radiosonde ascent of 2022-02-05 12Z, station 47412, the night of the record snowfall. This page grows the 2-D basal plane; columns and needles (−4 to −10 °C) live out of its plane and show up here only as slow, stubborn hexagons.

The Daily Fable · day 33