Influence of Precipitation on the Surface Energy Budget during Rain-on-Snow Events in the Mid-Atlantic United States

The rapid melting of a seasonal snowpack has several hydrologic, ecological, and societal impacts, particularly when rainfall contributes to the melt. These events, known as “rain-on-snow” (ROS), can cause severe flooding events, such as when several centimeters of rain and a deep snowpack contributed to the death of more than 30 people and resulted in millions of dollars of damage in January 1996 throughout north-central Pennsylvania. Although these events have been examined throughout the world, little research has focused on the importance of rainfall to the snowmelt process, particularly in the mid-Atlantic and northeastern U.S.

Using a synoptic typing method (i.e., the Temporal Synoptic Index), common patterns of lower- to mid-tropospheric circulation and associated surface meteorological data are extracted for ROS events in the mid-Atlantic region. Using a one-dimensional snow model, the surface energy budget components and melt rates during ROS events are compared among synoptic types. In addition, a sensitivity analysis of the impact of rainfall during ROS is conducted by removing liquid precipitation in a set of simulations. Results suggest that the impact of rain depends on synoptic type, indicated by the difference in turbulent fluxes among common ROS synoptic types. Specifically, synoptic types with higher temperatures and higher precipitation rates (e.g., a Weak Carolinas Low) show larger variability in sensible and latent heat fluxes between the rain and no-rain scenarios, and in turn, tend to be associated with more melt than compared to synoptic types with lower temperatures and comparable amounts of rain (e.g., a Great Lakes Low). Through a better understanding of the influence of rainfall on the snowmelt process, better prediction of severe ROS-induced flooding events are possible.