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Glossary Index

Avalanche Institute

 

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Graupel

Also: "Soft Hail"

A form of precipitation which looks like round pellets. Macroscopically, graupel resembles small beads of polystyrene.

Graupel is subject to rolling and can collect in pockets. It can also form a layer with a great deal of pore space and poor bonding. The pellets themselves are snowflakes which accumulated rime ice as they fell through certain atmospheric layers.

Graupel can sometimes form a weak layer in the snowpack which can fail and cause an avalanche. However, because it rolls the layer may not be consistent over a wide area. If there is no firm bed surface underneath and/or an insufficient slab above it may also cause a collapse of the snowpack without a slab avalanche. A graupel layer usually stabilizes within a couple days or less.

All crystal habits can acquire rime in the atmosphere - plate, dendrites, columns and needles. When there is enough rime to call it graupel the original crystal form is no longer visible.

Meteorologists once used the term "soft hail" but no longer do.

Rime on Plate Crystal

  

Graupel
A plate type crystal with rime on it.   Graupel. Original crystal habit can no longer be determined.
All micrographs are by the USDA and as government products made with public funds are in the public domain.

This glossary is a work in progress and is made possible by AlpenPro.