Mesoscale Discussion 1858
   NWS Storm Prediction Center Norman OK
   0905 AM CST Thu Dec 17 2020

   Areas affected...Eastern New York...southern Vermont...southern New
   Hampshire...northern Massachusetts...and southwest Maine

   Concerning...Heavy snow 

   Valid 171505Z - 171900Z

   SUMMARY...Heavy snowfall will likely continue for portions of New
   England through 18 UTC as the synoptic low begins to exit the
   region. Hourly snow rates between 2-3 inches per hour will continue
   in the near term, but should begin to abate through the late morning
   and early afternoon.

   DISCUSSION...Mid-morning regional radar imagery continues to show
   persistent organized snow banding from the Albany, NY region
   eastward through southern VT/NH and into southwest ME. This banding
   remains supported by the combination of ascent within the left-exit
   region of the upper-level jet and more focused ascent within a zone
   of mid-level frontogenesis/deformation around 700 mb. 12 UTC
   soundings from Albany, NY and Gray, ME show the dendritic growth
   zone remains roughly within the 700-600 mb layer where strong ascent
   is occurring. This is yielding a swath of observed snowfall rates
   between 2-3 inches per hour, which should continue for the near term
   (roughly the next hour or so). 

   While the environment remains supportive for heavy snowfall in the
   near term, RAP mesoanalysis trends have shown a gradual weakening in
   700 mb frontogenesis in tandem with the weakening of the synoptic
   low over the past 4 hours. This trend is reflected in MRMS
   precipitation rate estimates, which have been in decline since the
   11-12 UTC time frame. As the low continues to weaken and move
   offshore, the potential for widespread/persistent heavy snowfall
   rates will decline as well. Morning ensemble guidance suggests that
   the heavy snowfall potential should come to an end for eastern NY/VT
   by around 16-17 UTC, and should exit the southern NH/southwest ME
   region by 17-19 UTC. Given the recent observed trends noted above,
   these estimates appear reasonable.

   ..Moore.. 12/17/2020

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

   ATTN...WFO...GYX...BTV...ALY...

   LAT...LON   43397376 43537326 43807198 44027092 44207009 44146936
               43816936 43606993 43187045 42907099 42877184 42777326
               42597384 42587446 42897456 43137433 43397376