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| Heavily
rimed new snow, often shaped like little Styrofoam balls. |
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Graupel:
Graupel is that Styrofoam ball type of snow that stings your
face when it falls from the sky. It forms from strong convective
activity within a storm (upward vertical motion) caused by the
passage of a cold front or springtime convective showers. The
static buildup from all these falling graupel pellets sometimes
cause lightning as well.
It looks and behaves like a pile of ball bearings. Graupel is
a common weak layer in maritime climates but more rare in continental
climates. It's extra tricky because it tends to roll off cliffs
and steeper terrain and collect on the gentler terrain at the
bottom of cliffs. Climbers and extreme riders sometimes trigger
graupel avalanches after they have descended steep terrain (45-60
degrees) and have finally arrived on the gentler slopes below
(35-45 degrees)--just when they are starting to relax. Graupel
weak layers usually stabilize in about a day or two after a
storm, depending on temperature.
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Graupel
Summary:
Caveat:
Graupel tends to become faceted easily when subjected to a strong
temperature gradient, in which case, graupel produces avalanches
much more persistently.
Looks like:
Little Styrofoam balls
Feels like:
Stings your face
Behaves mechanically:
Like ball bearings
Distribution pattern:
Rolls off of cliffs and steep slopes and collects on gentler
terrain and in pockets. Not aspect or elevation dependent.
Persistence:
Sstabilizes about one day after deposited, depending on temperature
and metamorphism
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