Use of Radar for Spatial Snow Mapping: Implications for Water Supply Forecasts

Water supply forecasts in the West rely largely on data from over 700 SNOw TELemetry (SNOTEL) sites in the Western United States. Forecast methodology is based on 30-yr regression periods using SNOTEL and measured run-off. However, SNOTEL data represent point values and are rarely sufficiently clustered to depict the true 3-dimensional spatial distribution of snowfall. Furthermore, many headwaters basins do not have SNOTEL sites. Thus the lack of observations can result in large uncertainties in the forecasts. This paper presents a case study from a gap-filling radar project that targeted the San Juan Mountains in Southwest Colorado. For the Animas River Basin the additional radar observed a 10-fold increase in the snow water equivalent compared to surrounding NEXRAD radars. In addition the radar depicted the spatial distribution of precipitation. While the location of the radar was not optimal, radar quantitative precipitation estimates were very similar to SNOTEL precipitation amounts at most SNOTEL locations.