Area Forecast Discussion
Issued by NWS Blacksburg, VA

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389
FXUS61 KRNK 062338
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
638 PM EST Tue Dec 6 2016

.SYNOPSIS...
Low pressure will pass northeast of the region and weaken
overnight. A weak cold front trailing this system should move across
the area late tonight into early Wednesday. High pressure builds
east in the wake of this front by Wednesday afternoon followed by
a stronger cold front that should cross the region on Thursday.
&&

.NEAR TERM /THROUGH WEDNESDAY/...
As of 230 PM EST Tuesday...

Low pressure in Eastern Kentucky this afternoon will continue to
weaken as it marches northeast tonight. Meanwhile, Coastal low off
the North Carolina will deepen tonight and push out into the
Atlantic ocean overnight into Wednesday.

The best dynamic lift will occur this afternoon into this evening
ahead of a negatively tilted shortwave trough lifting northeast
through the southern Appalachians. After the surge of PVA passes,
then precipitation will wane with rain tapering off from southwest
to northeast. Water vapor loop showed drier air pushing in from the
southwest this afternoon into tonight. Gradual clearing will follow
for most of the CWA tonight as winds become northerly behind the
departing storm system. Lingering clouds and light precipitation
will be found across the mountains, with potential for drizzle and
or freezing drizzle for the West Virginia Highlands. Used a blend of
NAM and continuity to capture the pops for tonight. Utilized the
SREF temperature profiles to shape the weather grids. Added areas of
fog especially in the east tonight. Low temperatures tonight will
range from around 30 degrees in northwest Greenbrier county to the
upper 30s in the Piedmont.

Light wintry mix of lingering precipitation across western slopes of
Greenbrier County Wednesday morning will taper off by afternoon.
High temperatures will vary from around 40 degrees in the northwest
mountains of Southeast West Virginia to the mid and upper 50s in the
Piedmont.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
As of 245 PM EST Tuesday...

Brief quiet period under zonal flow aloft Wednesday night will quickly
transition to one of eastern troughiness with a subsequent Arctic
front crossing the region from northwest to southeast on Thursday.
Models remain rather inconsistent in the degree of return moisture
ahead of the boundary starting later Wednesday night and with the
actual 850 mb front Thursday. Not seeing a lot of support to
include much precip but given some slight backing as well as
possible slowing of the front, think prudent to keep in some low
pop mention espcly southwest sections under the tail of a passing
jet streak. This would consist of mainly a rain/snow shower mix to
just spotty rain showers south/east pending timing of the cold
advection, followed by a switch to mainly post frontal upslope
snow showers later in the day. Kept temps mostly in the 30s
Wednesday night as clouds/mixing increase with a range of highs
from steady mid 30s northwest, to 40-45 Blue Ridge, to low 50s
southeast Thursday pending timing of the actual frontal passage.

Cold advection will dominate the remainder of the period as strong
northwest flow continues ahead of high pressure building slowly east
from the central U.S. Guidance remains in line in showing winds just
below advisory levels most spots Thursday night into Friday while
dropping 850 mb temps down to as low as -15C mountains. However with
the core of the Arctic air sliding by to the north, should be warmer
out east of the ridges given less pronounced digging of the trough off
latest runs. This would support blustery lows in the mid/upper teens
mountains to low/mid 20s east with western wind chills zero to 10
above. Appears to be just enough low level moisture coinciding with the
coldest air aloft and stronger upslope flow to result in periods of
snow showers mainly far northwest. However since coverage iffy given
such mixed/dry air, only including a low pop northwest slopes into
Friday for now. Otherwise expecting a mainly sunny but cold and continued
blustery day Friday outside of the upslope western zones where more
clouds may persist. Appears highs will stay below freezing for much
of the mountains Friday, while rebounding into the 30s to around
40 piedmont where cold advection offset by downsloping flow will
occur.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
As of 130 PM EST Tuesday...

Upper trough lifts out Friday night allowing cold surface high pressure
to build overhead by Saturday morning. This should bring diminishing
winds overnight but also good radiational cooling within the residual
piece of Arctic air in place. Still some potential to see warm
advection high clouds invade late Friday night into Saturday morning
which could keep readings from bottoming out. Thus running with mostly
clear and lows teens mountains to upper teens/low 20s east for now.

Surface high should cross the region Saturday with a fast zonal flow
regime developing that will continue into early next week. Exodus of
the cold pool aloft should allow for gradual moderation in temps into
the 30s to lower 40s Saturday before much stronger warm advection on
southwest flow develops Sunday into Monday ahead of an approaching
upstream cold front. Latest models have slowed down the eastward
progression of deeper moisture with this initial front similar to the
earlier ECMWF with most pops holding off until Sunday night or Monday.
This should be after warming aloft has won out with mostly chance
rain/showers with perhaps some snow mixed in far west/northwest. Lots
of uncertainty moving ahead toward midweek in whether or not a punch of
dry air follows this boundary before the next northern stream wave
approaches Tuesday, or does it stall with moisture returning back north.
For now will dry things out on day7 per WPC and latest 12Z ECMWF with
overall temps 40s west to 50s north Monday/Tuesday.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 625 PM EST Tuesday...

Poor flying conditions expected to persist through tonight with
improvements on Wednesday.

Widespread rainfall from earlier has tapered to mainly drizzle
this evening under developing areas of fog that will likely
persist much of the night. Thus still expecting periods of IFR at
most terminals overnight with potential for LIFR vcnty of the
mountains, with ridges obscured in stratus. A weak secondary cold
front will cross the western mountains overnight allowing for a
gradual transition to elevation snow showers in West Va, with
drying elsewhere toward daybreak as deeper northwest flow
develops.

Better drying will continue early Wednesday resulting in a return
to VFR along/east of the Blue Ridge Wednesday morning, with
improving conditions likely delayed until afternoon at KBLF/KLWB
given residual low level upslope moisture. Should finally see all
sites become VFR during Wednesday afternoon under some high clouds
and northwest winds at 5-15 kts, perhaps gusting to near 20 kts at
times over the mountains.

Low to medium confidence in ceilings, visibilities and winds
during the taf period.

Extended aviation discussion...

Clouds and possibly a few showers may return Wednesday night in
advance of an approaching Arctic front that is expected to move
through the region Thursday. Limited moisture may result in a few
rain or western snow showers in advance of the boundary Thursday
morning. However upslope conditions should support snow showers
across the mountains behind the front Thursday afternoon into
Friday along with a significant surge of cold air. This will lead
to VFR conditions east of the Blue Ridge through much of the
period beyond Thursday, but MVFR conditions may linger into Friday
across the West Va sites. West to northwest winds behind the front
will be strong into Friday with gusts likely topping 25-30 kts at
times. Winds and any residual low level cloud cover should quickly
fade by Saturday as high pressure builds overhead making for
overall VFR conditions this weekend ahead of the next cold front
that wont arrive until early next week.
&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...KK
NEAR TERM...KK
SHORT TERM...JH
LONG TERM...JH
AVIATION...JH/KK/PM



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