Snow
Classification of snowflakes

Micrography of thousands of snowflakes from 1885 onward, starting with Wilson Alwyn Bentley, revealed the wide diversity of snowflakes within a classifiable set of patterns. Closely matching snow crystals have been observed.

Ukichiro Nakaya developed a crystal morphology diagram, relating crystal shapes to the temperature and moisture conditions under which they formed, which is summarized in the following table.

Nakaya discovered that the shape is also a function of whether the prevalent moisture is above or below saturation. Forms below the saturation line tend more toward solid and compact while crystals formed in supersaturated air tend more toward lacy, delicate, and ornate. Many more complex growth patterns also form, which include side-planes, bullet-rosettes, and planar types, depending on the conditions and ice nuclei. If a crystal has started forming in a column growth regime at around −5 °C (23 °F) and then falls into the warmer plate-like regime, plate or dendritic crystals sprout at the end of the column, producing so called "capped columns".

Magono and Lee devised a classification of freshly formed snow crystals that includes 80 distinct shapes. They documented each with micrographs.
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