A Polarimetric and Microphysical Investigation of the Northeast Blizzard of 8-9 February 2013

On 8 February 2013, two low-pressure systems merged over the northeastern United States, producing a historic winter weather event that ranked among the top five worst blizzards in the region. Heavy snowfall and blizzard conditions occurred from northern New Jersey, inland to New York, and northward through Maine. Storm-total (8-9 February 2013) snow accumulations of 30-61 cm were common, with amounts exceeding 61 cm over a SW-NE-oriented region from Long Island, New York to southern Maine. Maximum accumulations up to 102 cm, as well as snowfall rates exceeding 15 cm hr^-1, were reported in parts of Connecticut. In addition to record-setting snow accumulations, significant coastal flooding and hurricane-force wind gusts were recorded along the coast, with a peak gust of 40 m s^-1. Impacts of the event included at least 18 fatalities, thousands of flight cancellations at major airports, travel bans, and hundreds of thousands of customers throughout the region left without electricity for several days.

Measurements from dual-polarization radars provide valuable insight into the microphysical processes within storms. A preliminary investigation of polarimetric observations during this event reveals several intriguing features, including a distinct localized downward excursion of the melting layer bright-band to the surface (characterized by reduced ρ_hv and locally maximized Z_H and Z_DR), an abundance of radial streaks of enhanced positive and negative Z_DR due to depolarization of the transmitted radar signal, a “flare echo” or three-body scatter signature suggesting the presence of hailstones, and Z_H as high as 60 dBZ in a region of thundersnow over Connecticut. Additionally, there were numerous signatures of enhanced Z_DR located above the environmental freezing layer, which were associated with enhancements in K_DP and slightly reduced ρ_hv. These enhanced Z_DR values signified the presence of large, horizontally-oriented ice crystals in the subfreezing temperatures aloft, primarily due to lack of aggregation. The evolution of the aforementioned signatures are observed using data from the WSR-88D S-band polarimetric radar in Upton, NY (Long Island; KOKX) between 1100 UTC 8 February 2013 and 0300 UTC 9 February 2013.

This study investigates the origin and nature of these distinctive polarimetric signatures and the thermodynamic conditions within which they developed, using environmental thermodynamic data obtained from the experimental High-Resolution Rapid Refresh (HRRR) model. These data are used to interpret the polarimetric signatures of different types of ice crystal habits (e.g., needles, plates, stellars, and dendrites), which form in regimes of differing temperature and ice supersaturation. Additionally, polarimetric signatures at the surface are analyzed alongside observations of meteorological Phenomena Identification Near the Ground (mPING) surface data for verification of radar-indicated winter precipitation types.

Currently, the microphysical properties of winter storms have largely been unexplored, as polarimetric investigations have been focused on warm-season and severe convective storms. Yet, with the recent polarimetric upgrades to the United States WSR-88D network, ample dual-polarization data are now available for locations throughout the country, allowing for abundant observations of the microphysical properties of winter precipitation. The results of this study will further understanding of the fundamental microphysical processes within winter storms, as well as aid in improvement of the representation of winter precipitation in numerical modeling.