Snow graces the winter sky in many different forms. We have large lazy flakes drifting down, sharp needles driven by harsh winds and thick curtains that swiftly blanket the landscape. Late winter storms offer good chances to observe one of our more unusual and distinctive kinds of snowfall; “graupel”. Graupel – that sounds like some kind of respiratory malady, doesn’t it? Also known as soft hail or tapioca snow, graupel consists of tender round snow pellets no bigger than a pea. The name comes from the German word for hulled grain, “graupe”.
Graupel accompanies warmer winter storms, the kind we often have in March, as well as during summer showers high in the mountains. The pellets form when snow crystals fall through a low cloud of super-cooled liquid droplets. The foggy droplets readily coalesce and freeze around the falling ice crystals, accumulating to form soft graupel pellets. The process is somewhat akin to making rock candy from a concentrated hot sugar syrup, or the method used to generate artificial snow. In contrast, sleet forms when raindrops fall through a cold air layer and freeze.
Our big snowfalls are spawned by storms that generate sprawling unbroken cloud decks. Graupel snow, on the other hand, tumbles down from the bellies of fluffy cumulus clouds. As a consequence, squalls of graupel are brief, the pellets accumulating in a thin white bumpy layer, hence the other common name, “tapioca snow”. A buried layer of tapioca snow is prone to avalanche for the first day or two, after which the pellets anneal and stabilize. Any connoisseur of Utah snow should have graupel in their lexicon of wintry terminology, at the ready to impress any Sun Belt visitor met on the slopes.
This is Linda Kervin for Bridgerland Audubon Society.
Photos: Courtesy & Copyright Jim Cane
Text: Jim Cane & Linda Kervin, Bridgerland Audubon Society
Riehl, Herbert: Introduction to the Atmosphere, McGraw-Hill Book Company, 1972 http://www.amazon.com/Introduction-Atmosphere-Herbert-Riehl/dp/0070526567
Rime and Graupel http://emu.arsusda.gov/snowsite/rimegraupel/rg.html
American Meteorological Society, Glossary of Meteorology http://amsglossary.allenpress.com/glossary/search?id=graupel1
Graupel – What is Graupel? http://weather.about.com/od/g/g/graupel.htm