Monday, January 10, 2011

Calling All Snow Geeks

University of Utah Atmospheric Sciences Professor Tim Garrett and engineer Cale Falgatter have developed a system that takes photos of falling snowflakes and measures their fall speed.  There are a host of possible applications for this system, including the validation and improvement of forecasts by numerical weather prediction models.

Alta Ski Area and The Center for Snow Science at Alta post images of flakes during winter storms on the Snowflake Showcase web page at  Below are samples of a couple of stellar dendrite aggregates from Saturday night.  Stellar dendrites have a lot of pore space and can produce a snowfall with very low water content.  The Utah Avalanche Center reported that the snow that fell Saturday night had a water content of less than 3%.  Cold smoke.

Photo: University of Utah/Center for Snow Science at Alta
Photo: University of Utah/Center for Snow Science at Alta
Snow with a water content of 4% or less is called wild snow by meteorologists (Judson and Doesken 2000, p. 1579).  Many storms in the Wasatch conclude with a period of wild snow, but deep powder days (i.e., days with at least 10" of new snow) with a mean water content of 4% or less are fairly rare.  In other words, major storms consisting almost entirely of wild snow are rare even in the Wasatch.  At Alta, for example, only 6% of the deep powder days have a mean water content of 4% or less.

Tim and Cale are working on a new and improved system that will enable 3-D imaging.  Add real-time access, and we're going to be able to look at evolving winter storms in a whole new way.  One thing that you notice quickly when looking at these images (or snowflakes falling during winter storms), is that the vast majority of snowflakes have taken a beating and are very difficult to categorize.  Pristine crystals are the exception and not the rule.

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