Observations of a Northern Plains snowfall

On 15-16 March 2005, an Alberta Clipper moved through Eastern North Dakota spreading a band of light snow over the area. The Department of Atmospheric Sciences at University of North Dakota (UND) owns and operates a C-band polarimetric Doppler weather radar. The department has also established an atmospheric observatory with the purpose of providing high-resolution surface measurements of various atmospheric variables from the surface to the mid-troposphere. The site is located 65 km to the SE of the radar. Precipitation characterization is an important component of on going research. In particular, a video disdrometer is located at the site to examine the variations of hydrometeors of both snow and rainfall. Both instruments were continuously sampling during the snowfall event that occurred on 15-16 March 2005. This event seemed ordinary except for a distinct transition zone in the snowfall properties that was observed in the radar differential reflectivity (ZDR) field. The transition from near zero/positive ZDR to negative ZDR occurred along a very distinct line in the snow band. Observations from the video disdrometer along with hand photographs of crystal type and visual observation of the snowflake shape and fall motion led to the determination that the transition was caused by a change in snowflake type versus a distinct crystal habit change.