The Thermodynamic and Microphysical Evolution of an Intense Snowband during the Northeast U.S. Blizzard of 8–9 February 2013

Abstract

n intense snowband developed across Long Island, New York, to the north and west of the surface cyclone center on 8?9 February 2013. The snowband evolved through three distinct phases during its 12-h lifetime. During phase 1 the band developed in an area of low-to-midlevel frontogenesis and pivoted over central Long Island and southern Connecticut, where it remained for approximately 10 h. The environment surrounding the snowband cooled to <0°C; however, the band was collocated with a 900?700-hPa layer that remained above 0°C for ~5 h. During phase 2 the band exhibited heavy snowfall rates exceeding 7.5?10 cm h?1 with large and aggregated snow, wet-growth hail-like particles, and a radar reflectivity of ~55 dBZ. About 1 h later during phase 3, the snowband reflectivity decreased to near 30 dBZ and was characterized by less dense snow in a colder environment while still maintaining heavy snowfall rates (6.5?6.7 cm h?1). The Weather Research and Forecasting (WRF) Model was used to analyze the band and temperature evolution. Model trajectories terminating within the warmer snowband environment underwent rapid ascent on the east side of the band during which condensation and deposition enhanced the warming before undergoing rapid descent within the band. Analysis of the thermodynamic equation within the band environment revealed that this subsidence warming and upstream condensational heating for trajectories entering the band partially offset the diabatic cooling term, which supported a warmer layer and mixed precipitation during phase 2. Finally, model sensitivity tests showed that melting helped cool low levels and change the microphysical character to all snow during phase 3.