Cataloging Snow Band Vertical Structure: Insights from NASA IMPACTS and NEXRAD Data

We use radar data from the NASA Investigation of Microphysics and Precipitation for Atlantic Coast-Threatening Snowstorms (IMPACTS) field campaign and from NWS WSR-88D network to examine the 3D structures of snow bands during January and February of 2020, 2022 and 2023. Combined analysis of the vertically-pointing airborne radar data from IMPACTS and the horizontally-scanning operational radars allows us to identify and catalog locally-enhanced linear bands in reflectivity in time sequences of horizontal regional maps that were sampled during NASA IMPACTS airborne radar flight legs. The high spatial resolution of the NASA airborne radar reflectivity and Doppler velocity data reveals details that are not discernible from the coarser vertical resolution NWS volume coverage patterns. Snow particles fall at about 1 m/s and usually take over an hour to traverse from near cloud top to the surface. During that time, the trajectory of a falling particle can bend and twist as it falls through layers with different wind speeds and directions and moves 10s of km horizontally. The wind patterns within winter storms yield complex 3D structures in reflectivity that are tilted and smeared and often substantially dispersed before they reach the surface.

Figure 1: Horizontal and vertical reflectivity of a snow event on February 5th, 2020 from 22:52:39 to 22:58:44 UTC. The left image is a regional composite of 0.5 degrees PPI NEXRAD scans with a green line marking the ER-2’s flight leg. The red circle notes where the snow band is located. The right image is a vertical cross-section of reflectivity from the EXRAD radar on the ER-2. The white shape highlights the vertical structure of the snow band. The black markers indicate the center of the snow band above and below the 2 km shear layer.