Needles
Needles are formed at the upper end of the temperature spectrum,
usually when ground temperatures are at or near the freezing point.
To grow, these crystals need an air temperature in the -5 to -10
degrees C range. Needles tend to produce a dense, stiff snow pack
which can produce an avalanche under the right conditions.
The series is based on the 1951 International Commission on Snow
and Ice classification system. The commission produced a fairly
simple and widely used classification system for solid
precipitation. This system defines the seven principal snow crystal
types as plates, stellar crystals, columns, needles, spatial
dendrites, capped columns, and irregular forms. To these are added
three additional types of frozen precipitation: graupel, ice
pellets, and hail. The classification is the least complicated in a
series of snow classification systems. The most complex
classification scheme, an extension of Ukichiro Nakaya's work, was
published by meteorologists C. Magono and C. W. Lee in 1966. Their
system included 80 different snow crystal types.
Twenty years ago I used the international classification in an
Independent Physics Field Study where I observed snowflakes for the
winter and developed correlations with surface and lower
atmospheric conditions.
Today, the classification system is used here to find structures
in nature that look similar to the snow referenced in the cache
name.