Precipitation intensity during rain-on-snow

Mid-winter rainfall onto established snowpacks has the potential to generate high stream flows and flooding. Rain-on-snow can also increase the potential for snow avalanche. Precipitation intensity is a vital piece ofinformation when forecasting and assessing stream flow and snow stability during rain-on-snow. Precipitation intensity during 120 rain-on-snow storms from the past 21 winters at the Central Sierra Snow Laboratory in the Sierra Nevada of California were analyzed. These data were used to generate both storm and seasonal recurrence intervals for varying mid-winter rainfall intensities. Mid-winter rainfall intensities were found to range between less than 1 mm/hr to over 27 mm/hr with a mean of 2 mm/hr. Mean maximum rainfall intensity was found to be 5 mm/hr for approximately 5 hours. An average annual maximum rainfall rate of 8 mm/hr has a recurrence interval of approximately 3 years.