What an amazing storm. A manual analysis of storm total snowfall accumulations for 08-09 February 2013 shows that 24″+ snow accumulations largely occurred in a SW-NE oriented band from Long Island to southern ME, with the heaviest accumulations (up to 40″) occurring primarily in central CT. I’m not too familiar with the topography and climatology of New England, so, I hope that the below analysis is reasonably accurate.
The maximum in CT appears to be connected with an intense, persistent band of convection
that was at peak intensity between roughly 01-03Z on February 09th. SPC mesoanalysis data suggests that thermal profiles over CT should have been entirely at or below freezing between 01-03Z. The 00Z OKX RAOB showed a thermal profile below freezing from the surface to 900 mb. We can’t be completely sure above 900 mb since the balloon had problems when it ran into heavy precipitation and a 60+ knot LLJ, though it seems reasonable that thermal profiles were isothermal/freezing at warmest in CT. Dual pol radar imagery from KOKX during that time is very interesting. Initially (0206Z), southern portions of the band over CT were characterized by very low CC values, on the order of 0.80-0.90, with ZDR values as high as 2-4 dB and Z values between 45-50 dBZ. In this environment, dual pol reference tables indicate that CC values were indicative of large, wet aggregates and ZDR values were indicative of very wet snow. Over time, by 0259Z, CC values increased to 0.96-0.99 and ZDR values decreased to 0-1.5 dB, suggesting less aggregation and drier snow. It would be interesting to see how snowfall rates changed during this time, and whether or not the change in dual pol characteristics between 0200-0300Z were related to a change in the intensity of the convective band, the rapidly changing environment /thermal structure/ associated with strong cold advection on the western periphery of the deepening cyclone, or (perhaps more likely), both?
I’ve been in touch with Paul Schlatter, who is much better with dual pol interpretation than I am, and he sent the following comments: