Mesoscale Discussion 1856
   NWS Storm Prediction Center Norman OK
   0912 PM CST Wed Dec 16 2020

   Areas affected...Extreme northeastern PA...parts of southern/eastern
   NY...northern CT...western and northern MA...southern NH/VT

   Concerning...Heavy snow 

   Valid 170312Z - 170915Z

   SUMMARY...The primary band of persistent heavy snow will orient from
   southern/east central NY across northwestern MA to southern VT/NH
   through the early morning hours, with 2-3 inch per hour rates
   expected through 09-12z.

   DISCUSSION...A 1002 mb surface cyclone along the MD coast will
   continue northeastward through early Thursday morning, just off the
   southern New England coast.  Very strong low-midlevel warm advection
   has contributed to heavy snowfall the past several hours across
   parts of PA/NY into southern New England.  A warm nose in the
   850-700 mb layer (temperatures near or just above 0 C), and ocean
   influences near the coast have resulted in mixed precipitation
   spreading northward across NJ and Long Island, and this trend will
   continue into coastal areas of southern New England overnight. 
   Additionally, the midlevel dry slot has reduced saturation in the
   dendritic growth zone (generally 600-500 mb layer) from south to
   north, which has reduced snowfall intensity and also contributed to
   mixed precipitation types.

   Northwest of the dry slot, the longer-duration heavy snow is
   expected, with some banding structures and embedded convection in
   association with weak static stability and focused frontogenesis in
   the midlevels.  Here, ascent will be maximized in the dendritic
   growth zone for several hours and temperature profiles will remain
   well below 0 C, which will support snowfall rates of 2-3 inches per
   hour through about sunrise.

   ..Thompson.. 12/17/2020

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...GYX...BOX...BTV...ALY...BGM...CTP...

   LAT...LON   41787741 42607602 43287410 43647232 43417121 42717070
               42347092 42057096 41867133 41707342 41667422 41517520
               41197695 41377735 41787741