Microphysical Characteristics of Snowbands along the U.S. Northeast Coast Using In Situ Surface and Radar Observations and Simulations

Snowbands are challenging to predict and can have major societal impacts. One uncertainty with these bands is the complex microphysical processes, which are not well understood. Microphysical and mesoscale characteristics associated with snowbands passing through the central Long Island (LI) were observed from 2017-2019 using Ka-band scanning polarimetric radar, multi-wavelength profiling radar, lidar, microwave radiometer, disdrometer, and snow camera measurements located at Stony Brook University (~100 km east of New York City on north shore of Long Island). Four of the 12 snow storm events during this period were associated with single or multiple snowbands. The goal of this analysis is to better understand the microphysical special variations and evolutions in and around the snowbands for these winter storms, and to compare with some high resolution Weather Research and Forecasting (WRF) runs.

Generating cells were commonly observed near the cloud tops, while dominant ice growth processes within the clouds were complex and highly variable for snowbands, with unrimed/rimed aggregate and/or graupel particles often observed at the ground. The radar polarimetric and Doppler spectrum measurements identified aggregation and riming signatures in clouds accompanying the snowbands that produced intense radar reflectivity. The riming process was identified as turbulence signatures in Doppler velocity and spectrum width and increases in particle fall speeds, consistent with rimed particles observed by the snow camera. Those riming signatures tended to be found in association with easterly to southerly winds at low levels. The aggregation signatures were identified as changes in polarimetric variables from a height with a temperature around -15°C toward the ground and slower fall speeds of ice particles. Large values of dual-wavelength ratio of S-band NEXRAD radar reflectivity to the Ka-band radar reflectivity were observed in a snowband, suggesting that the large snowflakes dominated, consistent with less rimed, large aggregates observed by the snow camera. These aggregation signatures tended to be observed with westerly to northerly winds. The WRF was simulated for 1-2 of these events down to 1-km grid spacing around LI using a few different initial conditions and different microphysics. This presentation will highlight some of the similarities and differences between the WRF and observations for these snowbands.