Microscale Updrafts Within the U.S. Northeast Coastal Snowstorms Using High-Resolution Cloud Radar Measurements

Limited knowledge exists about ~100 m scale precipitation processes within U.S. Northeast coastal snowstorms because of a lack of high-resolution observations. We investigate characteristics of microscale updraft regions within the cyclone comma head and their relationships with snowbands, wind shear, frontogenesis, and vertical mass flux using high-spatiotemporal resolution vertically-pointing Ka-band radar measurements, soundings, and reanalysis data for four snowstorms observed at Stony Brook, NY. Updraft regions are defined as contiguous time-height plotted areas with upward Doppler velocity without hydrometeor sedimentation that is equal to or greater than 0.4 m s^-1. Most updraft regions in the time-height data occur on a time scale of seconds (< 20 sec), which is equivalent to spatial scales < 500 m. These small updraft regions within cloud echo occur more than 30% of the time for three of the four cases and 18% for the other case. They are found at all altitudes and can occur with or without frontogenesis and with or without snowbands. The updraft regions with relatively large Doppler spectrum width (> 0.4 m s^-1) occur more frequently within midlevels of the storms, where there is a moist shear instability layer. The updraft regions produced higher mass flux when they are closer together in space and time. The higher values of vertically-integrated upward mass flux within updraft regions often occur during snowbands with background ascent from frontogenesis.