Thundersnow over the Northeast U.S. can occur in conjunction with coastal cyclones, Alberta Clippers, lake-effect storms, and elevation storms, and is hypothesized to result from the contributions of dynamical and thermodynamical processes to thundersnow development. The particular processes important to the development of thundersnow appear to be strong dynamic and/or orographic lifting and elevated convection with surface temperatures near 0°C. These processes motivate the construction of a thundersnow phase space to assess the relative importance of dynamical versus thermodynamical forcing in generating thundersnow in various synoptic-scale flow regimes. Thundersnow cases spanning 19942013 will be identified from archived METAR surface observations and NLDN data. WSR-88D and dual-polarization radar data will be used to identify possible convective signatures associated with the thundersnow cases. The NCEP CFSR(v2) gridded datasets will be used to populate the aforementioned phase space and construct the various composite and case study analyses.
The occurrence of thundersnow relative to low-level and upper-level jets and jet-related vertical circulations also will be analyzed. Sounding and cross-section analyses will be produced using RUC hourly 13-km datasets. These datasets will be used to determine the CAPE profiles attending thundersnow. In cases where there are slantwise updrafts in the presence of high concentrations of ice crystals, minimal CAPE thresholds required to enhance updrafts and induce charge separation and lightning will be quantified. The frequency of thundersnow events in the absence of CAPE also will be assessed, and minimal ascent and ice crystal thresholds required for thundersnow to occur in nonconvective events will be quantified.