Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 071447

Area Forecast Discussion
National Weather Service Blacksburg VA
947 AM EST Wed Dec 7 2016

High pressure will build across the Mid Atlantic states today
providing fair weather. An arctic front will cross the region
Thursday, a much colder airmass overtaking the region for the
remainder of the week.


As of 947 AM EST Wednesday...

Made some minor adjustments to temperatures for this morning with
sfc obs and trended towards lav for early this afternoon. High
pressure will build into our area today. Under plenty of sunshine,
high temperatures will climb into the upper 30s in the northwest
Greenbrier to the upper 50s in the Piedmont. Clouds increasing
tonight ahead of an approaching arctic cold front with lows from
the mid 20s in the west to mid 30s in the east.

As of 530 AM EST Wednesday...

Beneficial rain from Tuesday will be followed by dry high pressure
today. East of the Blue Ridge skies will be sunny with mild
afternoon temperatures (50s). Clouds will linger across the
mountains early this morning, erroding fore noon temperatures
rebounding into the 40s.

Changes will begin to take place tonight with clouds increasing
ahead of an approaching arctic cold front. This front is the
leading edge of some very cold air, originating from Canada and
the blizzard stricken northern plains.

Models hint of some very light precip (mainly trace amounts) associated
with the arctic front with light snow showers western slopes and
potential for a few sprinkles and/or virga along leading edge of
the airmass change for the VA/NC piedmont toward daybreak
Thursday. Temperatures tonight will dip into the 30s, which will
be warm, relatively speaking compared to the temperatures that
will occur the next several nights to follow.


As of 430 AM EST Wednesday...

Primary focus during the short-term period is the passage of the
modified Arctic front and associated post-frontal, unseasonably cold
air and breezy to gusty winds Thursday night and Friday.

Daily details follow...

Thursday: Trend in 00z model guidance suite continues to point to a
dry frontal passage. The 850 mb front passing across the forecast
area, reaching eastern Virginia by early afternoon. Expect cloud
cover to erode rather quickly in the post-frontal airmass except in
the favored southeast West Virginia counties where stratocu will be
more difficult to shake free of. By the afternoon, period of strong
cold air advection then begins as 850 mb temps fall to -6 to -12C.
Moderately strong 3-hourly pressure rises during the 21-00z period
along with northwesterly 850 mb winds of 35 knots supports
increasing wind speeds of 15 to 20 mph, with gusts as high as 35 mph
mainly across the hilly terrain. Highs in the 30s west of the Blue
Ridge to the upper 40s/low 50s in the southeastern/southside
Virginia areas, timing of which will be staggered to some extent by
the passage of the front. In other words, trend in temps is pretty
much all downhill once the front clears.

Thursday Night: Thursday night stands to be one of the coldest
nights yet experienced this early winter season, by all indications.
Shallow moisture profile but enough in the -12 to -18C snow growth
layer across western Greenbrier into northern Summers counties to
support at least some light snow showers, but given the shallow
moisture depth and limited progged lift in that layer, I suspect
there won`t be much if any accumulation at all in these areas.
Otherwise, variably cloudy skies with cold advection continuing in
earnest. Conditions should stay relatively breezy as cold advection
aloft should help to maintain relatively steep low-level lapse
rates. Given low temperatures ranging from the teens to the mid 20s
and winds of 15 to 20 mph, wind chills drop into the single digits
to the teens. While not excessively cold, make sure to reach for the
hat and coat as it should be the first cold evening thus far in the

Friday: Ridging continues to build in as center of large high
pressure sets up over the Mississippi River Valley. Any leftover
stratocu/areas of snow showers or flurries in southeast West
Virginia should begin to burn off with the daytime sun. Though 850
mb temps begin to moderate to values around -9 to -13C, it will
still be some 10 to 15 degrees colder than normal on Friday as highs
temps only top out in the 20s west to the upper 30s/near 40s in the
Virginia southside and the North Carolina piedmont.

Friday Night: Large high pressure continues to advance east to near
western West Virginia. While wind speeds should be lightening as
pressure gradient relaxes, clear skies and dry airmass should allow
for strong radiational cooling. Lows should dip into the teens to
perhaps the low 20s areawide, but it wouldn`t surprise if some of
the customarily colder locations such as Burke`s Garden drops into
the single digits.

Saturday: We should finally start to moderate temperature-wise with
surface ridge and weak mid-level height rises aloft over the
southern and central Appalachians. 850 mb temps on Saturday should
run about -6 to -9C according to the GFS, which with abundant sun
should push maxes into the 30s to mid 40s.


As of 330 AM EST Wednesday...

Stronger warm advection on southwest flow develops late Saturday
night 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.


As of 700 AM EST Wednesday...

Trend toward VFR for all terminals today. Northwest wind flow has
scoured moisture just east of Blue Ridge. Low Cigs/Vsbys still
persist over eastern VA/NC, and along the western slopes of the
Appalachians, but improving trend also expected for these areas
between now and noon.

For the 24 hour TAF Period 0712/0812...

DAN...VFR, Tempo IFR VSBY until 14Z.
BLF...MVFR CIG until 16Z, then VFR.
LWB...VFR, Tempo MVFR CIG before 18Z.
BCB...VFR, Tempo MVFR CIG before 15Z. MVFR CIG dvlpng aft 09Z Thu.

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

Extended aviation discussion...

An Arctic front will pass through the Mid-Atlantic Region
Thursday. System is moisture starved, but still may produce a few
rain/snow showers in advance of the boundary Thursday morning, and
virga with potential for a few sprinkles across the VA/NC
piedmont. After the frontal passage, cold blustery conditions will
develop for Thursday night into Friday, with upslope snow showers
along the western slopes of the Appalachians. MVFR cigs will be
found across the mountains with VFR east of the Blue Ridge. Tempo
MVFR vsbys will be associated with the -snsh. 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.
Next weather system to follow will be a cold front, models
suggesting a Sunday Night arrival.




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