Evolution of an Intense Mesoscale Snowband During the 8–9 February 2013 Northeast U.S. Blizzard

A mesoscale snowband during the Northeast U.S. extratropical cyclone of 8–9 February 2013 resulted in a narrow swath of accumulations greater than 76.2 cm (> 30 in) across Long Island and southern New England with observed snowfall rates in excess of 3 in h^-1. There were many socio-economic impacts, including the shutting down of major highways due to abandoned, buried vehicles and heavy snow and high winds causing 700,000 customers to lose power throughout the region. The evolution and structure of this snowband warrants investigation because of the observed range of radar reflectivity from > 55 dBZ at the peak of the band's apparent intensity to around 30 dBZ within 1 h.

The Weather and Research Forecasting (WRF) model was used to simulate the event down to 1.33-km horizontal grid spacing. Model output was verified with observational data including soundings, microphysical surface observations at Stony Brook, NY (SBNY), a vertically-pointing radar at SBNY, and the KOKX dual-polarization radar at Upton, NY to assess the processes responsible for the genesis and intensity of the mesoscale snowband, as well as its thermodynamic and microphysical structure and evolution.

The snowband developed to the northwest of the cyclone center collocated with the area of maximum 700-mb frontogenesis. The complexity is found in the microphysical structure as evident from the evolution of radar reflectivity values observed as well as differential phase shift (PhiDP) and the correlation coefficient (CC). The band was associated with rimed aggregates of dendrites, which became more rimed and mixed with sleet as the band intensified. The highest reflectivities were associated with gradients in PhiDP and CC values of 0.9 indicative of mixed-phase precipitation. The rapid disintegration of the 50+ dBZ reflectivities and rapid decrease in snow riming is hypothesized to be due to the merger between the coastal cyclone and the continental cyclone that disrupted the deformation in the lower troposphere, reducing frontogenesis, and weakening the band. Another hypothesis is that the character of the hydrometeors changed as the thermal structure changed with the introduction of colder, dryer air. The WRF was able to realistically simulate the band evolution, and a few microphysical schemes will be compared with the radar and in situ observations.