Symmetry of Snowflakes  surface bump...................dendrite
...........complex snowflake     With more water molecules
reaching the bump, the bump grows faster.  In a short time, the
bump sticks out even farther than it did before, and so it grows
even faster.  We call this a branching instability -- small
bumps develop into large branches, and bumps on the branches
become sidebranches.  Complexity is born.   This instability is
a major player in producing the complex shapes of snow
crystals.And since the ambient atmospheric conditions are nearly
identical across the crystal, all six budding arms grow at
roughly the same rate.     The temperature seen by the snow
crystal is not constant in time, however, since the crystal is
being blown about and is thus carried over great distances in a
cloud.  But the crystal growth rates depend strongly on
temperature.  Thus the six arms of the snow crystals each change
their growth with time, reflecting the ever-changing conditions
in the cloud.  And because each arm