Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 052011

Area Forecast Discussion
National Weather Service Blacksburg VA
311 PM EST Mon Dec 5 2016

An area of low pressure in the Gulf of Mexico lifts northeast
tonight and reaches the Appalachians Tuesday resulting in
widespread rainfall overnight into late Tuesday. Moisture pulls
off the coast Tuesday evening allowing weak high pressure to build
in from the Midwest on Wednesday. A strong cold front will cross
the region on Thursday.

As of 230 PM EST Monday...

In the wake of this morning shortwave, west winds were relatively
quick in eroding the lower clouds out. High pressure over the Ohio
Valley late this afternoon will build east this evening and reach
southern New England tonight.

Moisture will surge northeast tonight as low pressure over the
western Gulf of Mexico strengthens and moves northeast along a
stationary front. Despite the dry air across our region, WSR-88d
regional radar images showed rain lifting into Tennessee and western
North Carolina. Felt that the fastest models,including the HRRR, RAP
and SREF were too quick with drier airmass in place. Used a NAM
blend with GFS for pops tonight. Incorporated the temperatures
aloft for weather type.

The challenge tonight is whether or not clouds will trap any of
the afternoon warmth permitting slightly warmer readings overnight
before the rain arrives. Since some of the models are
entertaining the idea of some light wintry precip for the VA and
WV highlands, a 1 or 2 degree temperature flucuation could make
the difference between a cold rain versus some light
sleet/freezing rain for the Shenandoah valley and the VA/WV
Highlands. No winter weather advisories for tonight because any
sleet or ice accretion should be minimal, only adhering to
elevated surfaces as opposed to the ground (ground temperatures
still too warm to permit travel issues). Low temperatures tonight
will vary from around freezing mark to the lower 40s in the

A strong cold wedge east of the Appalachians will remain in place
Tuesday morning as low pressure moves northeast with strong
isentropic lift including upper dynamic support. A coastal low
pressure center will develop off the North Carolina coast Tuesday
afternoon. Widespread precipitation will continue through the
first part of Tuesday before starting to taper off during the
afternoon. There is enough warm air advecting in Tuesday to
transition any light wintry mixed precipitation in Greenbrier Cty
West Virginia and the Alleghany Highlands to all rain. A light
glaze of ice or coating of snow may possible at the highest
elevations. High temperatures Tuesday will range from the mid 30s
in the northern mountains to the mid and upper 40s in the south.

As of 215 PM EST Monday...

Surface low along the coast should exit Tuesday evening ahead of a
secondary trailing cold front that will help boot out residual deep
moisture overnight. However enough lingering wrap around rainfall to
keep chance to low likely pops going early Tuesday night espcly western
third as well as the far northeast sections with rain tapering
elsewhere. Will see a band of more shallow nature moisture along the
cold front that looks to cross the far west after midnight and the Blue
Ridge by early Wednesday. Appears enough to warrant a chance of added
showers western slopes overnight with a gradual transition to higher
elevation snow showers late as 850 mb temps fall below 0C.
Otherwise clouds lingering mountains with downslope clearing
east and lows mainly 30s.

Wednesday into Wednesday night will be the in between period separating
a more zonal trajectory from the impending digging upstream 500 mb
trough associated with the upcoming Arctic cold shot. Models even
suggest a period of warm advection in the afternoon under sunshine as
the flow backs from a weak northwest trajectory to southwest later in
the day. This should also push highs into the 50s from the Blue Ridge
east and close to 50 west. Flow deepens from the south/southwest
Wednesday night with guidance suggesting enough moisture return for a
few late night showers south/west, that should transition to snow
showers far west early Thursday when the Arctic front nears.

Front then crosses from northwest to southeast Thursday with cold
advection/upslope driven snow showers western mountains and
possibly a few sprinkles east. However moisture appears much less
today off models per overall westerly flow, so cutting back on
pops, but leaving in some mention given light QPF showing up off
ensembles. High temps Thursday tricky pending timing of the 850 mb
front, with a possible range from 30s west to around 50 Piedmont,
before falling with a slightly slower trend likely the best bet
with the frontal passage.

As of 130 PM EST Monday...

Strong cold advection will be ongoing to start the period as Arctic air
pours in ahead of high pressure that should shift east from the central
U.S. early Friday to about overhead the region by Saturday morning.
However latest models tending a bit weaker with the associated upper
trough per less digging that likely will keep the core of the Arctic
airmass to the north. This also along with very dry air advecting in
should help limit the degree of upslope snowfall behind the front as
the strongest northwest winds will only coincide with the coldest air
aloft Thursday night into Friday at best before moisture fades.
Thus going with only low pops northwest mountains Thursday night
with coverage gradually decreasing Friday. Elsewhere should remain
mostly clear but still cold and blustery into Friday evening with
overnight wind chills near zero across the higher ridges. Still
appears that Saturday morning will see the coldest temps as the
high settles overhead, although increasing high clouds may
curtail good radiational cooling per latest warmer guidance.
Otherwise lows mostly teens to near 20 mountains both nights, and
20s east with highs 20s to low 30s mountains Friday, to mid 30s to
lower 40s east.

Trough lifts out later Saturday with fast zonal flow aloft developing
Sunday into Monday as the surface high shifts east with
warming/moistening return flow developing. This will allow pieces of
energy ejecting out of the Rockies to perhaps bring some chance of
precip by late Sunday into Monday at this point. However guidance shows
considerable spread with consensus having a stronger northern stream
wave push a weak surface front with faint southern connection toward
the region by Monday. This could bring some chance of precip to mainly
the western counties by Sunday evening per faster GFS despite residual
low level dry air. Appears this would be mostly rain Sunday night into
Monday given column warming with possibly some mix late Sunday pending
timing. However quite iffy espcly given much slower timing off
the 12z ECMWF. Should see temps rebound into the upper 30s/40s
Sunday and 40s to mid 50s Monday as warm advection aloft reaches
the surface.

As of 1242 AM EST Monday...

High pressure to our north will provide brief drying this
afternoon before rain returns tonight and Tuesday. Lower clouds
associated with this mornings shortwave have eroded and moved
east into the Atlantic ocean.

Moisture will quickly return tonight. Low pressure over the
western Gulf of Mexico is progged to move northeast, rain
overspreading the region from southwest to northeast during the
overnight, reaching western NC after midnight, then into the
Virginias Tuesday morning...and associated with widespread IFR

Northwest winds northwest 5-10kts this afternoon, will become
light northeast after 21Z/4PM, before increasing again during the
overnight from the southeast as the storm system approaches from
the southwest.

Rain will continue Tuesday with widespread IFR/LIFR conditions.
A brief period of IP or freezing rain may be possible across the
northern mountains, mainly Greenbrier and Bath counties. However,
temperatures warm up quickly Tuesday morning. Not expected any
problems at taf sites.
Medium confidence in ceilings, visibilities and winds during the
taf period.

Extended aviation discussion...

Rain associated with IFR/LIFR conditions Tuesday afternoon into
Tuesday night will be followed by partial clearing Wednesday.
This break in the weather will be followed by a cold front
Thursday, this front bringing a surge of cold air. Look for a
return of sub- VFR conditions, this time associated with snow
showers across the mountains Thursday night into early Friday.

Friday, expect a gusty day across the region with lingering
upslope cloud and snow showers between KBLF-KLWB. East of the Blue
Ridge, VFR is expected.




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