Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 191440
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
940 AM EST Sun Nov 19 2017

.SYNOPSIS...
Much colder air on blustery winds will arrive today, with
clearing skies across the Piedmont, but with abundant clouds
over the mountains along with some upsloping snow showers across
the western flanks of the Appalachains. High pressure builds in
from the southwest late tonight into Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 938 AM EDT Sunday...Only noticeable change made to the
going forecast was to force more -RA/-SN as opposed to pure
-RA in the grids for today. Radar showing narrow bands of light
returns in the strong northwesterly cold advection, which have
been leading to intervals of rain or snow showers per METARs in
the mountains of western Summers, Mercer and Greenbrier
Counties, the Mountain Empire to about Wytheville, and into
Ashe, Alleghany and Watauga Counties. As surface temperatures
are near or just above freezing, this is probably a wet/low-SLR
type snow and limited accumulations reflected in the forecast
appear to be holding up. Expect intervals of snow showers to
predominate these areas, perhaps extending as far east as Giles
and Craig Counties. It`s a little milder but drier in the
Piedmont.

From a messaging perspective, will continue to carry the Wind
Advisory through to its expiration at noon since it is still
breezy, though the strongest winds capable of causing damage
have already passed. Recent gusts at Boone in the low- 40s MPH
are pretty much the strongest gust observations through the
last couple hrs this morning. Doppler profiler winds this
morning indicate a gradual downward trend. Also do note some
wave clouds around the mountains seen in visible imagery, so
certainly should be bumpy for aircraft flying aroud the
mountains. Do expect another uptick in winds/gusts with the
passage of the secondary shortwave trough now over IL/IA later
tonight but appears to be to just sub- Advisory levels.

More to come later...

Previous near-term discussion issued at 220 AM follows...

500MB trof deepening over the eastern United States this morning.
GOES16 water vapor loops showed a well defined short wave crossing
into Virginia early this morning. A second vorticity maximum will
track across the area late this afternoon into early this evening.
Colder air aloft will provide some instability today and strong
upslope northwest wind behind the cold front will result in a
prolonged period of showers along the west slopes of the
Appalachians.

No change needed to wind advisory at this time. Expecting strong
cold air advection this morning and 6hr pressure rises of 14 to 18
mb. By this evening pressure rises slacken but the second short wave
will bring another brief increase of the low level jet which will
extended the gusty conditions. Will be leaning toward NAM Nest and
MET guidance for lows tonight.

Temperatures will be in the 50s ahead of the front this morning then
drop behind the cold front today. High temperatures for most
locations in southwest Virginia, southeast West Virginia and
northwest North Carolina will be in the morning.

Much of the HiRes guidance has the pre-frontal showers into central
Virginia and North Carolina by 09Z/4AM, leaving only showers in the
mountains for the rest of the day. Models diminish upslope flow and
low level moisture after 03Z/10PM this evening. Snow showers will
taper off to flurries by midnight but cloud cover will take until
around sunrise to dissipate.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
As of 218 AM EST Sunday...

Upper pattern stays transitory this period, with a shortwave ridge
Monday over the west side of the mountains, then next trough digs
into the upper Great Lakes with broad troughing southward into the
lower Mississippi Valley, early Tuesday. At the surface high
pressure moves from overhead Monday to off the NC coast Monday night.
Will see some increasing moisture in southwest flow but models
overall keep us dry, with main surge of deeper moisture passing over
the southeast Tuesday. Cannot rule out a few showers as we head into
Tuesday night across the east, and with the next front over the
west, but looks marginal.

Models are showing a split flow regime midweek with northern stream
trough over the Northeast-Mid-Atlantic with west southwest flow
aloft over our forecast area, with a digging shortwave moving into
the mid and lower MS Valley Wednesday-Wednesday night. At the moment
models are keeping the deeper moisture and showers well south going
during this time across the Gulf Coast states, but may bear watching
if the the shortwave stays further north, which could push some rain
toward our southern forecast area Thanksgiving.

Overall, temperatures will be close to normal for lows and at or
below normal for highs. May see some uptick in winds from the
northwest as northern wave pushes across Wednesday per latest ECM.

&&

.LONG TERM /THURSDAY THROUGH SATURDAY/...
As of 300 PM EST Friday...

GFS ensemble indicates a 500 mb pattern resembling a cold season
positive Pacific-North American (PNA) teleconnection regime centered
around the Thanksgiving holiday period. This often translates to
mean troughiness at 500 mb into the central and eastern US, as
repeated shortwave troughs round the top of a large ridge across the
Pacific Coast and dig/reinforce cyclonic flow aloft. Overall an
unsettled holiday period but nothing that would significantly hamper
travel plans attm.

Kept highs for the Thanksgiving holiday only in the 40s with
partly cloudy skies and dry conditions.

Looks to be a warming/moderating trend to temperatures Friday into
the holiday weekend and will likely trend temperatures to near/above
late-November normals. Weather pattern then turns more unsettled
after the holiday weekend with a larger degree of guidance solution
spread.

&&

.AVIATION /14Z SUNDAY THROUGH THURSDAY/...
As of 545 AM EST Sunday...

A cold front extended from central New York through southern Georgia
and had crossed through KLYH and KDAN as of 10Z. Winds were from the
west to northwest with gusts of 15 to 25 knots. Cloud cover was
clearing rapidly east of the Blue Ridge with MVFR clouds along
the western slopes.

Strong upslope winds will  result in prolonged MVFR rain or snow
showers on the western slopes of the Appalachians, including at KLWB
and KBLF today. Any snow accumulation at these airports will be
light. Winds gusts will be as high as 40 knots, especially at higher
elevations this morning, then will gradually diminish this afternoon
and evening. After midnight the pressure gradient will slacken and
wind gusts will drop off then less than 20 knots at most locations.
As the winds diminish upslope precipitation will end. Several models
show low level moisture and resulting cloud cover eroding across
southeast West Virginia and southwest Virginia late tonight.

High confidence on the winds, ceilings and visibilities today, but
medium confidence on the timing of how quickly ceilings over the
mountains will improve to VFR tonight and when wind gusts will
diminish.

Extended Discussion...

Mainly VFR conditions are expected Monday into Friday.
Exceptions would be some lower cigs with a front/trough Tue
night-Wed in the mountains, and again Thanksgiving.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...Wind Advisory until noon EST today for VAZ007-009>020-022>024-
     032>035.
NC...Wind Advisory until noon EST today for NCZ001-002-018.
WV...Wind Advisory until noon EST today for WVZ044-507-508.

&&

$$
SYNOPSIS...WERT/WP
NEAR TERM...AL/AMS
SHORT TERM...WP
LONG TERM...AL
AVIATION...AMS/KK


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