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Mesoscale Discussion 164
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MD 164 graphic

   Mesoscale Discussion 0164
   NWS Storm Prediction Center Norman OK
   0855 PM CDT Tue Mar 20 2018

   Areas affected...Portions of WV and western/central VA

   Concerning...Heavy snow 

   Valid 210155Z - 210800Z

   SUMMARY...A band of moderate to heavy snow will develop
   northeastward across WV and western/central Virginia this evening
   and overnight. Snowfall rates around 1 inch per hour are likely,
   especially in the higher terrain.

   DISCUSSION...A shortwave trough will pivot northeastward across the
   Mid-Atlantic this evening/overnight, while a large-scale upper
   trough over the OH/TN Valley transitions to a closed low. Forcing
   for ascent preceding the shortwave trough will encourage development
   and deepening of a surface low off the NC/VA coast through the early
   overnight hours. A separate area of weak low pressure will remain
   over WV/far southwestern VA. A front will extend between these two
   lows, with a cold low-level airmass in place across much of the
   Mid-Atlantic to the north of the front.

   Moderate to heavy precipitation is ongoing this evening across
   southwestern VA into parts of WV in association with the previously
   mentioned shortwave trough. The 00Z sounding from Roanoke, VA shows
   a modest (around 3.7 degrees C) low-level warm nose centered around
   820 mb. As mid-level temperatures cool with the shortwave trough
   passage, the low-level thermal profile is likewise forecast to
   quickly fall below freezing across WV and parts of western/central
   VA. Indeed, recent surface observations and mPING reports across
   southwestern VA are indicating a fast transition from rain to snow,
   with some sleet mixed in at the leading of the precipitation shield.

   Continued east-northeasterly winds in the surface-850 mb layer will
   enhanced uplift along the Blue Ridge and Appalachian Mountains this
   evening and overnight. Snowfall rates of 1 inch per hour appear
   likely across much of the discussion area, especially in the higher
   terrain where this low-level uplift will be maximized. Most recent
   high-resolution guidance is in reasonable agreement in the placement
   of this moderate to heavy snowfall axis through about 08Z.
   Precipitation may lessen/shift farther eastward after this time as
   the coastal low develops northeastward over the western Atlantic and
   the shortwave trough moves away from this region.

   ..Gleason.. 03/21/2018

   ...Please see for graphic product...


   LAT...LON   36998146 37498166 37918170 38398135 38708084 38878036
               38907998 39057954 39317912 39457873 39457833 39327795
               38877784 37997819 37257893 36777983 36608045 36658104

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