Mesoscale Discussion 1875
   NWS Storm Prediction Center Norman OK
   0128 PM CST Thu Dec 24 2020

   Areas affected...southern and central Appalachians

   Concerning...Heavy snow 

   Valid 241928Z - 250000Z

   SUMMARY...Heavy snow is forecast to develop behind a cold front this
   evening. Low visibility and rapid accumulation from snow rates of 1
   to 2 inches per hour will be likely.

   DISCUSSION...Afternoon water vapor imagery showed a deep upper low
   and expansive area of cyclonic flow across much of the eastern US.
   At the surface, 19z analysis showed a cold front progressing
   eastward across the southern Appalachian highlands. Along the front
   a developing wave cyclone was observed across northeastern Georgia
   and southeastern Tennessee. Increasing lift from an embedded
   shortwave trough within the larger upper low should help intensify
   the developing surface cyclone as it rapidly moves north along the
   front into the central Appalachians this afternoon. With increasing
   pressure falls expected to develop along the frontal zone, enhanced
   cold advection in the low levels should rapidly cool the atmospheric
   column to support snow development by late this afternoon. Lingering
   instability from steep mid-level lapse rates, strong lift along the
   front, and enhanced convergence from windward side upslope flow
   should support moderate to heavy banded precipitation to the
   immediate west of the cold front. Snow rates of one to two inches
   per hour will be possible (especially along the crest of the
   Appalachians) through this evening. The heaviest snow is forecast to
   develop along a relatively narrow corridor 21-23z across portions of
   eastern Ohio/Kentucky into central West Virginia as the shortwave
   trough ejects overhead. A narrow corridor of mixed precipitation may
   also develop as the cold front begins to push to the east though any
   ice or sleet accumulations are forecast to remain minor.

   ..Lyons/Guyer.. 12/24/2020

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

   ATTN...WFO...RNK...PBZ...RLX...GSP...MRX...JKL...ILN...

   LAT...LON   35838348 36238354 37528326 38768281 39768212 40298164
               40388139 40398111 40178080 39748051 38918022 37788052
               36738132 36058188 35398278 35418326 35838348