Monitoring a rain-on-snow event

Most of the flooding and considerable erosion damage in the northwestern United States results from snowmelt during rain on snow events in the transient snow zone. Yet efforts to model snow accumulation and melt have concentrated on the deep or continuous snowpack regions. Equipment and procedures for measuring snow depth, snow water equivalent, and snowpack conditions in shallow and often drifted snowpacks, have not yet been adequately developed. This report describes an attempt to determine the water balance on small plots within a watershed during several snow accumulation and rain on snow melt periods. New equipment provides a means of obtaining estimates of evaporation from the snow cover. infiltration through frozen and unfrozen soils, and a photographic record of snowpack depth and coverage during the study periods. Results indicate that the equipment did provide good data for determining the water balance components involved. Evaporation rates compared favorably with previous studies and were generally ten percent or less of precipitation. Infiltration on the other hand varied from 0 to 100 percent of precipitaion depending on temperature, soil moisture, and snow cover conditions.