Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 240255

Area Forecast Discussion
National Weather Service Blacksburg VA
955 PM EST Mon Jan 23 2017

A deep low pressure system will continue to shift to the mid-
Atlantic Coast tonight. In the wake of the low pressure system,
a period of gusty northwest winds are expected for the North
Carolina high country and the Blue Ridge overnight into Tuesday
morning. Temperatures will rise well above normal for Wednesday,
but will trend closer to seasonal levels late in the workweek.


As of 920 PM EST Monday...

While radar trends have diminished over the course of the
evening there is still narrow bands of precipitation lined up
north to south from Southeast WV to the NC piedmont. Models
having a difficult time showing this in the near term and have
been pulling the main precip threat to the southwest VA
mountains overnight. This in line with upper pattern as sharp
vort max rotates southeast to the Southern and Central
Appalachians overnight. Temperatures sub-freezing in higher
elevations will lead to some snowfall, possibly freezing drizzle
or freezing rain if depth of moisture falls below the ice
crystal formation zone. The threat of a good snow is nil, but
some locations such as Mt Rogers, and Quinwood, WV are in line
to get about an inch of snow. Though temperature at the higher
elevations will be at or below freezing, a wet and warm ground
should prevent most roads from becoming slick, so not expecting
any hazards as far as snow goes.

As far as winds goes, still looks likely the low level jet
around 50 kts moves across the NC mountains between 06-12z and
with some decent pressure rises, as well as lowering inversion
should see some gusts close to 50 mph, in locations such as
Boone and West Jefferson. Also with wet soils, some weakly
rooted trees are likely to fall, so do not be surprised if some
power outages occur across the High Country and northward toward
Meadows of Dan late tonight into Tuesday morning.

No other major changes were needed with lows still mainly
ranging from upper 20s to lower 30s in the higher elevations to
lower 40s southeast.

Previous valid discussion...

Clouds will gradually decrease from east to west through the
night as drier air works into the area on the backside of the
departing low.

Clearing will continue through the day on Tuesday as high
pressure continues to work in from the west. Temperature
forecast remains somewhat challenging, moreso for the mountains,
as it will depend on the timing of clearing taking place. Have
portions of southeast West Virginia and far western Virginia
warming into the mid 40s during the afternoon, but admit this
may be a few degrees too optimistic. Further east, more
confident of temperatures warming into the mid and upper 50s
east of the Blue Ridge, where clearing early in the day will
allow for abundant sunshine.


As of 330 PM EST Monday...

Mid-level heights begin to rise significantly Tuesday night into
Wednesday, with leftover shallow moisture in the favored upslope
region in southeast West Virginia thinning out even further.
Forecast trends dry early Tuesday, lasting into a good part of
Wednesday as aforementioned mid-level ridge crests over the region.
Under plentiful sunshine and 850 mb temperatures between +9 and
+11C, Wednesday`s highs stand to be well above normal. Highs into
the 60s should be common across the forecast area, and a few point
locations east of the Blue Ridge may touch 70 degrees given
adiabatic downslope warming off the Blue Ridge.

Later Wednesday and into Wednesday night, we start to see modest mid-
level height falls associated with a broad, positively-tilted trough
with an associated surface front. Front itself moves across the
forecast area Wednesday into a part of Thursday. There are some
differences between the 12z global suite of models on the degree of
precipitation associated with the front, with the GFS and Canadian
GEM offering a slightly wetter forecast than the ECMWF depiction.
Given that there may be little moisture ahead of the front to work
with, sheared-out vort energy and limited progged surface
convergence, I`ve kept PoPs on the lower side - no higher than low
Chance - closer to the ECMWF idea. Strong cold advection behind the
front Thursday, modest post-frontal pressure rises and a
northwesterly jet of up to 45 kts will pose at least some risk for
at least breezy northwest winds, especially at elevations above 3000
feet. Cold advection aloft also forces northwesterly upslope
precipitation in southeast West Virginia, the Mountain Empire and
Grayson Highlands down into the North Carolina high country to
change from rain to light wet snow by late in the day Thursday.
Would expect little if any snow accumulation initially given the
prolonged stretch of mild temperatures we`ve had. While still
appears to be above-normal from a high temperature perspective - 40s
to low 50s - our 850 mb temperatures then start a downward trend
late in the day.


As of 330 PM EST Monday...

Our 500 mb height pattern begins to change in the mean to one of
cyclonic flow aloft late in the week through early next week. Such a
pattern lends itself to relatively unsettled weather conditions and
cooler temperatures - to values near or slightly below late-January

Indications from today`s global models continue to point to a rather
long duration northwest flow upslope snowfall starting Thursday
evening into the weekend, and strictly limited to the favored
western-facing hillsides in southeastern West Virginia, far
southwest Virginia and the high country of North Carolina. It does
appear that some light accumulations of snow would be possible
through much of this period. How much snow still remains in some
question as periods of more persistent snow would be governed to
some extent by embedded shortwaves in the broader cyclonic flow, and
largely westerly continental flow would also serve to keep available
moisture limited.

Outside of these upslope areas however, at this point it appears to
be a largely cooler and dry period with highs generally in the 30s
to low 40s and lows in the 20s.


As of 620 PM EST Monday...

Storms system starting to transfer to the coast this evening
and seeing a diminishing trend to the rain. Will continue to
deal with sub-VFR conditions this evening before northeast winds
shift northwest and bring an improving ceiling scenario to the
east of the mountains, including Roanoke and gradually
Blacksburg and Lewisburg. Will continue though to keep stratocu
and showers in the Bluefield area through Tuesday.

Northwest winds will be the main factor late tonight into
Tuesday as gusts to 25 to 35 kts are possible mainly in the
foothills and mountains.

Extended Aviation Discussion...

Winds will subside Tuesday night. High pressure will finally
spread into the region by Wednesday. A band of MVFR showers is
possible along/behind a cold front Thursday into Thursday
night. Colder west to northwest wind flow will develop behind
this front with mountain snow showers possible for the weekend
associated with MVFR CIGS/VSBYS.


VA...Wind Advisory until noon EST Tuesday for VAZ015>017.
NC...Wind Advisory until noon EST Tuesday for NCZ001-002-018.


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