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Mesoscale Discussion 79
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   Mesoscale Discussion 0079
   NWS Storm Prediction Center Norman OK
   0224 PM CST Sun Jan 16 2022

   Areas affected...Portions of the central Appalachians and southern
   Mid Atlantic.

   Concerning...Winter mixed precipitation 

   Valid 162024Z - 170130Z

   SUMMARY...Heavy winter precipitation is expected to increase in
   coverage and intensity across portions of WV/VA into MD and PA over
   the next several hours. Periodic snow rates of 1 to 1.5 inches/hour
   will be possible within the heaviest bands. A change over to mixed
   precipitation types including sleet and freezing rain will likely
   occur, supporting ice accumulations as well.

   DISCUSSION...2000 UTC surface observations fixed a 999 mb surface
   low along the NC/SC border. To the north, a broad band of precip has
   brought numerous reports of moderate to heavy snow across the
   Carolinas and southern VA over the past several hours. Regional
   water vapor/infrared imagery has shown a gradual expansion and
   northward shift of cooler cloud tops associated with the
   precipitation. This shift is coincident with the arrival of stronger
   height falls aloft from an approaching upper low suggesting large
   scale ascent is moving north. As the upper low continues to mature
   and move toward the northeast, the surface low should deepen,
   enhancing precipitation rates farther north into the Mid Atlantic
   and central Appalachians.

   Regional model sounding show cool and dry profiles that may take
   some time to saturate ahead of the initial precipitation.
   Evaporative and dynamic cooling should work to keep the profile cold
   for several hours ahead of increasing mid-level warm advection from
   the approaching low. The strong isentropic ascent will likely
   support snowfall rates of 1 to 1.5 inches per hour. Quick
   accumulation of snow along with poor visibility appear likely to
   develop from northwest VA, through MD, and into central PA. 

   However, after dark, very strong warm advection will begin to peak
   as several hours of warming enhance the mid-level warm nose despite
   cold surface temperatures. A rapid transition to mixed precipitation
   types and freezing rain is expected after 00z from southeast to
   northwest. A full change over to rain may also occur farther east,
   where mixing from the moderate to heavy precipitation, coupled with
   strong warm advection is likely to raise surface temperatures
   several degrees above freezing.

   Considerable uncertainty exists along the transition zone in regard
   to precipitation type and snow accumulations/rates. While most of
   the area will see at least brief heavy snow before transitioning,
   mixed p-types and the potential for freezing rain may support up to
   a tenth of an inch of ice accumulations.

   ..Lyons/Grams.. 01/16/2022

   ...Please see for graphic product...


   LAT...LON   38637916 38917956 39647962 40707913 41377862 41977709
               41887583 41617510 41447497 41137521 40567615 39927666
               38787718 38297733 38137780 38227827 38377862 38637916 

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