Area Forecast Discussion
Issued by NWS Blacksburg, VA-- Remove Highlighting --
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FXUS61 KRNK 011200
Area Forecast Discussion
National Weather Service Blacksburg VA
700 AM EST Thu Dec 1 2016
High pressure will build in from the southwest today into
Saturday. The high moves overhead Sunday though a storm system
developing over Gulf Coast states should begin to spread moisture
our way Sunday into Monday.
.NEAR TERM /THROUGH TONIGHT/...
As of 330 am EST Thursday...
Models keeping northwest flow today in the low levels with variable
solutions on extent of moisture and precip in the upslope area.
Seems moisture will be limited enough to keep isolated threat in the
Greenbrier Mountains. Temperatures favor a snow/rain shower mix, but
again little qpf so not expecting accumulations.
Winds should be brisk at times today across the mountains/foothills,
with gusts as high as 25-30 mph, to possibly 35-40 mph early in the
Temperatures will actually be near normal with highs from the 40s
mountains, to 50s east.
Tonight, the flow appears to weaken where winds tally off some,
though center of high stays over the Gulf Coast states. With upper
vort moving in the flow aloft across the mountains, some lift into
the mountains may allow for a slight chance for more snow showers in
the area west of Lewisburg, WV but again not much qpf if any.
Lows will stay at or above normal with lows from the upper 20s to
lower 30s mountains, to mid 30s east.
.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
As of 430 AM EST Thursday...
A brief period of zonal flow will be in place at the beginning of
this period as the previous upper low exits the northeast U.S. and
a southern stream upper low deepens across Mexico and south Texas.
This later system will be our next significant weather maker late
in the weekend.
For Friday...a very weak clipper system is evident in the WNW flow
aloft, which could support development or continuation of light
upslope snow showers. Support is minimal and the upper-level
pattern is not overly favorable, but will continue with a low
mentionable pop across western Greenbrier. Otherwise, mostly
cloudy west to mostly sunny Piedmont. Temperatures will be
seasonably cool as 850mb temps hover in the 0C south to -6C north
range, trending upward slightly Saturday. This will equate to near
to slightly below normal temperatures.
Saturday, high pressure will linger but expect extensive high
clouds to overspread the region as the southern stream system
begins to move east into Texas and the flow aloft becomes more
diffluent. The cloud cover and cool 850mb temps will keep surface
temperatures seasonably cold.
Sunday presents the biggest forecast challenge this period as the
southern stream upper low strengthens and moves into the Mid-
South and begins to take on a negative tilt. Strong isentropic
lift will develop Saturday night and spread into the southwest
part of the CWA as the southern stream system develops. With 850mb
temps at or below 0C yet at 12Z Sunday and a likely in-situ wedge
pattern, a period of snow or rain mixed with snow will be possible
across the western mountains of NC and VA before warmer air
arrives from the south. There are considerable differences between
the GFS and the NAM with regard to how quickly the column will
saturate, with the NAM much quicker to do so early Sunday. The
BUFKIT sounding for Boone shows good potential for snow at 12Z Sun
while the GFS shows a marked dry layer in place, not moistening up
enough for precipitation until afternoon, at which point the
entire forecast area is too warm for anything but liquid
precipitation. Hopefully later model runs will get a better
handle on this, but for now have continued with a mention of
rain/snow western higher elevation areas Sunday morning, changing
to all rain during the afternoon. Temperatures will remain just
below normal Sunday, but warm above the critical freezing level by
late morning/early afternoon even in the west, but will likely
struggle to do so at the rate the models advertise given the wedge
in place. QPF amounts Sunday will be light, mostly 1/2 inch or
less as the main system remains well to our southwest at this
.LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 445 AM EST Thursday...
The aforementioned Sunday event is just an antecedent short wave
ejecting from the deep southern U.S. low. The main show for our
region in assocation with this upper low will come later Monday
into Tuesday as the system finally lifts across the Appalachians
and Mid-Atlantic region. The strong negative tilt to the upper low
as it moves across the area will lead to significant PVA/upward
vertical motion and a good chance for a soaking rain, potentially
another inch or so.
Two concerns at this point are once again the potential for a
brief period of mixed rain/snow at higher/colder elevations west
of the Blue Ridge early Monday and the threat for thunderstorms
into Tuesday. With respect to the winter weather threat, this
looks to be less than what is possible on Monday as 850mb temps
continue to warm, but a brief rain/snow mix in western/higher
elevations cannot be ruled out around daybreak Monday. Later
Monday into Tuesday 850mb temps surge back into the lower double-
digits (e.g., +12C) with strong warm advection. However,
significant SVR parameter and CAPE all suggest any notable threat
for thunder will remain to the southeast of our CWA. Given this
last event, however, I would say the threat for thunder Tuesday is
non-zero at this point.
Temperatures will be much milder through the period with highs
warming into the 50s west and 60s east with lows only in the 30s
and 40s after Monday. After this system passes, a significant
surge of cold air, coldest of the season, looms to our west for
.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 650 AM EST Thursday...
Northwest flow will keep stratocu banked up across the mountains
for this period, resulting in mainly high end MVFR/low end VFR
cigs at BLF/LWB. Appears ROA/BCB will be scattered most of the day
though small period of bkn VFR cannot be ruled out.
Winds will be west to west-northwest at 8-13kts with gusts to
20-25kts...higher in the mountains from mainly 14z-23z.
High pressure will still be southwest of the region tonight though
winds speed should weaken some.
Extended aviation discussion...
High pressure enters the area Saturday into early Sunday with VFR
conditions. Will start to see moisture stream north from a storm
system moving across the Gulf Coast states Sunday into Monday with
increasing threat of mainly rain. Will likely see some sub-VFR
cigs and possibly vsbys at most sites by Monday.