The Value of Dual-Polarization Radar in Diagnosing the Complex Microphysical Evolution of an Intense Snowband

The northeast U.S. extratropical cyclone of 8–9 February 2013 produced blizzard conditions and over 0.6–0.9 m (2–3 feet) of snow from Long Island through eastern New England. A surprising aspect of this blizzard was the development and rapid weakening of a snowband to the northwest of the cyclone center with radar reflectivity factor exceeding 55 dBZ. Because the radar reflectivity within snowbands in winter storms rarely exceeds 40 dBZ, this event warranted further investigation. The high radar reflectivity was due to mixed-phase microphysics in the snowband, characterized by high differential reflectivity (ZDR > 2 dB) and low correlation coefficient (CC <0.9), as measured by the operational dual-polarization radar in Upton, NY (KOKX). Consistent with these radar observations, heavy snow and ice pellets (both sleet and graupel) were observed. Later as the reflectivity decreased to less than 40 dBZ, surface observations indicated a transition to primarily high-intensity dry snow, consistent with lower-tropospheric cold advection. Therefore, the rapid decrease of the 50+ dBZ reflectivity resulted from the transition from higher-density, mixed-phase precipitation to lower-density, dry-snow crystals and aggregates. This case study indicates the value that dual-polarization radar can have in an operational forecast environment for determining the variability of frozen precipitation (e.g., ice pellets, dry snow aggregates) on relatively small spatial scales.