The Role of Turbulent Heat Fluxes in Eastern U.S. Rain-on-Snow Precipitation

Due to the dual inputs of both liquid precipitation and melted snow, rain-on-snow precipitation poses a high risk for enhanced runoff and flooding. Even in ephemeral snow regions common to the eastern U.S., there have been many examples of rain-on-snow events resulting in loss of life and millions, or even billions, of dollars in damages. While research is extensive in the Mountain West of the U.S. where deep snowpacks are present, relatively limited research into the dynamical and thermodynamical forcing mechanisms driving rain-on-snow in the East has been conducted. Here, we present an assessment of multiple case studies of hourly energetic fluxes collected from three AmeriFlux observational sites during rain-on-snow precipitation events in the eastern U.S., covering the Connecticut, Ohio, and Missouri River Basins. Results suggest sensible and latent heat fluxes exhibit large negative (into the snowpack) fluxes immediately preceding the onset of precipitation that typically last multiple hours after precipitation ends. Daily aggregated sensible and latent fluxes can regularly exceed 650 Wm^-2 and 250 Wm^-2, respectively, compared to net radiative fluxes that typically remain less than 500 Wm^-2. In some cases, sensible or latent fluxes remain positive (away from the surface) during rain-on-snow events, but the magnitude is substantially diminished relative to the characteristic diurnal cycle of these fluxes. Collectively, the individual contributions of turbulent and radiative fluxes to the surface energy balance during rain-on-snow events were spatially variable and exhibited longitudinal-oriented gradients of increasing/decreasing fluxes; turbulent fluxes represented over 80% of energy inputs to the snowpack in the Connecticut Basin, compared to approximately 50% in the Missouri Basin, on average. This suggests independent of event magnitudes, there are differences in how rain-on-snow events are forced across the eastern U.S.