Synthesis of surface snowfall rates and radar-observed storm structures in 10+ years of northeastern US winter storms

Abstract. Winter storms can cause disruptions in the densely populated regions of the northeastern United States. Mesoscale snow bands embedded within winter storms are often the main focus of snowfall forecasts and analyses. While primary bands are associated with frontogenesis, multi-bands are found in environments with both frontogenesis and frontolysis. This study investigates the relationship between observed surface snowfall rates and local enhancements in radar reflectivity (i.e., mesoscale snow bands) using data from 264 storm days over 11 winter seasons (2012–2023). We compare hourly surface snowfall rates obtained by National Weather Service (NWS) Automated Surface Observing Systems (ASOS) weather stations with the area × time fractions of locally enhanced reflectivity features and of all echoes passing over the 25 km radius of the surface observation. Our analysis focuses on non-orographic snowstorms with surface winds < 5 m s−1. Our findings show that most of the time snow rates are low (75 % of hours had liquid-equivalent snow rates less than 1 mm h−1). Heavy snow rates (>2.5 mm h−1 liquid equivalent) are rare (<4 % of observations). When enhanced reflectivity features pass over a location, only 1 out of 4 h have heavy surface snow rates. High-spatial-resolution vertical cross-sections from airborne radar obtained during the NASA Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign and rapid-update range-height indicators (RHIs) from ground-based radar demonstrate that enhanced reflectivity features in snow aloft are tilted and smeared on their way to the surface as their constituent snow particles are dispersed laterally by the horizontal winds within the storm. The duration of all snow echo over a location is useful in determining where higher snowfall accumulations may occur.