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011
FXUS61 KRNK 130449
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
1149 PM EST Wed Dec 12 2018

.SYNOPSIS...
High pressure will remain over the region tonight ahead of a
weak cold front that will approach from the west overnight
before dissipating across the mountains on Thursday. A
developing low pressure system will eject northeast out of the
southern states Thursday into Friday before crossing the Mid
Atlantic region this weekend. High pressure follows this system
for early next week.
&&

.NEAR TERM /THROUGH THURSDAY/...
As of 845 PM EST Wednesday...

Lower level moisture continues to slide east across the
mountains tonight in advance of low pressure passing well to the
north, and ahead of a weak surface cold front entering the Ohio
Valley. Expect some of this cloudiness to spill east crossing
the Blue Ridge overnight before getting clipped by downsloping
westerly flow as seen via the evening RNK sounding aloft.
Soundings also show quite a bit of dry air in the low levels
which so far has acted to keep cloud bases higher, and the
northwest sections free of any freezing drizzle per forecast
shallow moisture beneath the mid level inversion. Latest
Nam/HREF still indicate the potential for some spotty very light
precip in southeast West Va overnight, so keeping in mention for
spotty freezing drizzle for now. Otherwise beefed up clouds
early on west, and kept things mainly cloudy outside of the
piedmont where appears skies will stay clear longer.

Temps remain quite varied given clouds/mixing mountains and
decoupling over snow pack in the valleys near the Blue Ridge and
outlying eastern locations. Appears most lows outside of the
piedmont to occur through midnight before steadying/rising
pending extent of the low clouds through dawn. Thus lowered
readings a few degrees where already at earlier forecast lows
before slowly rising as clouds arrive mountains, while keeping
the east also colder under better radiational cooling a bit longer.


Previous discussion as of 242 PM EST Wednesday...

High pressure over Georgia and Florida this afternoon will slide
east tonight into Thursday. Low pressure centered near Chicago will
drop southeast quickly tonight into Thursday. Plenty of high clouds
across the region enhanced by standing wave clouds downstream of the
southern Appalachians and high level moisture advection into our
region. Some low clouds will from in the mountains tonight. Shallow
moisture will advect into the western mountains late tonight. Bufkit
model sounding support the mention of slight chance of drizzle or
freezing drizzle in the northwest mountains late tonight. The NAM
and HiResW-ARw-East had some light return in the northwest mountains.
Low temperatures tonight will range from the mid 20s along the
southern Blue ridge to the lower 30s in the far west mountains. The
upper low center will slide from the Great Lakes to southern New
England on Thursday with mid to upper ridging building overhead. A
cold front will be approaching from the west Thursday. High
temperatures will vary from the lower 40s in the northwest to the
upper 40s in the southeast.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 242 PM EST Wednesday...

An active weather pattern is forecast to close out the end of the
week. High pressure over the northern mid Atlantic will transition
into a wedge Thursday night ahead of an approaching low pressure
system moving out of the lower Mississippi valley. Wedge of high
pressure is expected to keep shallow layer of cold air locked into
place within the boundary layer with a chance for some freezing rain
as precipitation overspreads the region by daybreak Friday.

Confidence in fine details of the temperature forecast and resulting
precipitation type is not high, but there is the potential for some
locations mainly north of Route 460 to pick up a light glaze of ice
early Friday morning before a transition to all rain. As the
precipitation advances, the low level wind field will become quite
energetic with some gusty winds expected at the higher elevations
west of the Blue Ridge, especially from the NC mountains up into the
Mountain Empire region of VA, and from Bluefield to Beckley in WV.

Per the 12Z model guidance primary focus for the heaviest rain from
this system will be late Friday into Saturday.  QPF of 1 to 2 inches
of rain seem to be common amongst the models with the heaviest
amounts occurring across the piedmont and tidewater regions of
VA/NC. However, upslope southeasterly low level flow is still
expected to enhance amounts near the Blue Ridge.

Flooding will become a concern by Saturday, but the big unknown with
respect runoff is how much snowmelt will take place.  The snowpack
may initially act as a catchers mitt with respect to rainfall
intercept, delaying potential runoff, especially if temperatures and
more importantly wet-bulb temperatures remain cold enough to
mitigate melting. This may be the case in the mountains, but for the
piedmont where warmer temperatures will occur, the chances for
flooding are much higher. Hydro ensembles continue to show a robust
response particularly along the Dan river so there is growing
concern for potentially significant flooding Friday night and into
the weekend for at least some of our rivers.

The vertically stacked closed low is forecast to move directly over
the region by Saturday night, keeping a good chance of showers
around with potential for some wet snow mixing in at the higher
elevations west of the Blue Ridge late Saturday night.

Temperatures will remain below normal through the end of the week
before trending upward a bit once the wedge breaks later in the
weekend.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 200 PM EST Wednesday...

Cutoff low will continue to impact the region Sunday. Even though
model simulations indicate the deeper moisture gets shunted to our
east, the presence of the cold pool aloft associated with the upper
low will result in scattered to numerous showers, with mainly rain
showers in the lower elevations Sunday, and potential for rain
mixing with or changing to snow showers across the mountains.

A northern stream shortwave is expected to give the cutoff low a
boot off the coast Monday with colder but dry weather resuming for
next week.

&&

.AVIATION /04Z THURSDAY THROUGH MONDAY/...
As of 1140 PM EST Wednesday...

Lower clouds within deep westerly flow continue to push east
across the region except in the southeast where downsloping is
acting to clip moisture crossing the foothills. This ahead of a
weak cold front that is pulling low level moisture northeast
into more of an upslope regime tonight. This supports MVFR
ceilings at KLWB/KBLF and perhaps at times at KBCB. More in the
way of VFR ceilings are expected at KROA/KLYH and only
scattered clouds around KDAN overnight. As the shallow moisture
increases cant totally rule out IFR ceilings espcly at KBLF with
some light drizzle and possibly freezing drizzle along the far
western slopes. However for now confidence/PoPs remain low so
keeping out any precip mention at this point. Dry weather will
continue into Thursday with warm advection helping to scour out
low level moisture leaving mostly VFR during the afternoon.
Moisture well in advance of a deepening low pressure system to
the southwest will increase Thursday evening with potential for
southeast flow upslope flow to produce MVFR/IFR ceilings prior
to midnight along the Blue Ridge.

Ceiling heights and exact timing of changes for the mountain
location is low to medium, however confidence is fairly high
that VFR conditions will prevail throughout for eastern
locations.

Extended Aviation Discussion...

A strong low tracks across the southern United States at the
end of the week. There are some timing differences in the models
but at this point the widespread rain and associated sub-VFR
conditions will be very late Thursday night into Friday. This
ahead of the low and a strong coastal warm front that will aid
lift across the region on Friday and result in widespread rain
and likely IFR or worse conditions by afternoon. Upper low may
then linger Friday night into Saturday with potential MVFR/IFR
lingering to start the weekend as added bands of showers work
north ahead of the upper system. Sct MVFR conditions in
showers and low clouds are still possible in the west on Sunday
in the wake of the departing upper low. Improving conditions to
VFR will then be on tap for Monday.

&&

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

&&

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