Disdrometer data use in analyzing blowing snow characteristics within the roadway environment

Blowing snow is the number one concern for maintenance officials and is one of the most prevalent weather phenomenons that affect winter driving. Understanding the physical and dynamical characteristics of the weather conditions that produce blowing snow are vital for improved prediction of this phenomena. It is also important to understand the influence the roadway environment has on the nature of blowing snow and the resulting reduction of driver visibility and formation of drifts along the road surface. Having an understanding of these features and their time dependencies is crucial information for maintenance personal and traveler safety. To achieve a better understand of blowing snow within the roadway environment it is necessary to develop improved methods to quantify the horizontal and vertical mass flux of snow. Within the present study video disdrometers are used to provide this valuable data. In the past video disdrometers have been used extensively in the study of liquid precipitation. The present research is applying video disdrometers to frozen precipitation following similar methods as with liquid precipitation. Disdrometers are placed at various heights adjacent to the road surface to provide data on crystal shape, size, and density at discrete time intervals. From these data the overall mass flux of snow across the roadway is determined. It is found that the vertical gradient in the mass flux of blowing snow is not uniform in the roadway environment and results in varying horizontal visibility with height. This is a significant influence on visibility of drivers of vehicles at differing heights. In this paper the research framework of the investigation is presented along with data collected from several video disdrometers that are part of an instrumented road weather research site. Measurements of the mass flux of snow during various blowing snow events are presented. The measurements are correlated with observed snowfall rate and accumulation using precision wind, snow depth, and precipitation measurements available from the road weather research site. A description of how this information is being used to support verification of current research into blowing and drifting snow prediction model development is also presented.