Radar Snowfall Estimation in Southern New England

Liquid equivalent of falling snow is an integral component of global precipitation and therefore water cycle. The amount of water within a snowflake can dramatically alter how much snow accumulates in a storm. Wet snow through a Nor’easter and dry snow through a cold frontal passage result in very different accumulation at the same snow intensity. This study investigates the empirical relationships between measured reflectivity (Ze) and estimated snow water equivalent rate (SWER), known as SWER(Ze) relationship, utilizing ground measurements in Southern New England. The field study was conducted under NASA’s Global Precipitation Measurement mission ground validation program and overlapped with the NASA’s Investigation of Microphysics and Precipitation for Atlantic Coast Threatening Snowstorms (IMPACTS) field campaign during the winter of 2021-22. Both SWER and Ze depend on the size, concentration, fall speed, and mass of the falling snowflakes; all measured or estimated by the Precipitation Imaging Package (PIP), which was designed and assembled at NASA Wallops Flight facility and the main instrument in this study. The key objective of this study is to provide the relevant SWER(Ze) relationship to create an accurate ground-based snowfall mapping for evaluating the spaceborne snowfall retrieval algorithms. This study derived and evaluated overall, event-by-event, density, snowflake habit based, synoptic, and High Resolution Rapid Refresh (HRRR) model parameter based SWER(Ze) relationships. The synoptic and HRRR model based SWER(Ze) relationships have potential to be used by National Weather Service and other operational forecasters for estimates of falling snow and related hydrological forecasting.