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ACUS11 KWNS 210156
SPC MCD 210155

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...


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