Climatology of crystal habits and degrees of riming for snow falling in the Cascade Mountains during two winter seasons

During the winters of 2006-2007 and 2007-2008, researchers from the University of Washington gathered observations of snow crystal habit types and degree of riming at a mountain pass in the Cascade Mountains of Washington state. Observations were made manually by stereomicroscope every 15 minutes during stormy periods. Additional observations of particle fall speeds, particle size distributions, and precipitation rate were collected by automated instruments. Approximately 500 hours of observations were gathered, yielding a good climatology of snow characteristics at this location. The purpose of the observations was to study habit-dependent and riming dependent characteristics of snow, such as fall speeds, size distributions, precipitation rate, and density and sheer strength of new snow accumulations; and to provide a verification data set for a habit and riming prediction capability we have added to a bulk microphysical scheme. This talk will offer an overview of the observations, including frequency of occurrence of different crystal habit types and degrees of riming in the Cascade Mountains; some new information on fall speeds for certain crystal types and its dependence on degree of riming; and dependence of the density of accumulated snow on particle habit type and degree of riming.