Area Forecast Discussion
Issued by NWS Blacksburg, VA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS61 KRNK 240152

Area Forecast Discussion
National Weather Service Blacksburg VA
952 PM EDT Wed Aug 23 2017

A cold front will continue to move southeast away from our
area tonight. A large high pressure system will move out of
central Canada and build eastward behind the front Thursday,
bringing significantly cooler temperatures to the region into
the weekend.



At 9 PM EDT, a cold front had moved well southeast of our
region leaving low level northeast or northwest winds ushering
in drier air. However, 65-70 F dew points still lurk across the
NC piedmont and VA southside along with a weak low level
convergence zone. Isolated showers continue to form along this
boundary in the southern shenandoah valley, and with surface
based CAPES still exceeding 1000 j/kg along the boundary,
retained a small chance for showers into the early evening.

Drier air doesn`t push into this area until late tonight,and
mesoscale models along with the NCEP Time lagged Rapid Refresh
Ensemble System develop clouds across the eastern portion of our
area tonight, which are already occurring per latest satellite
images. As a result, pushed up temps a few degrees in the east
for lows tonight.

Best chance for patchy fog given good radiational cooling
conditions is in the Greenbrier and New River Valleys where
winds will go calm/decouple quickest. Combination of at least
potential scattered clouds and enough northerly gradient flow to
the south and east should mitigate such development in our
southern and eastern counties.

A broad upper trough will slide east from the Great Lake
regions to the East Coast Thursday. This afternoon`s cold front
will continue to push south into the Southeast States. During
Thursday afternoon, a shortwave embedded within the broad upper
trough will rotate eastward into the Mid Atlantic Region. This
feature may create clouds to upslope areas of the Alleghanys,
with a few showers possible during peak diurnal heating. The NAM
was the furtherest south with the southern extent of the
isolated showers compared to ECMWF and GFS. High temperatures
Thursday will vary from the upper 60s in the northwest mountains
of Greenbrier county to the lower 80s in the Piedmont.


As of 230 PM EDT Wednesday...

Some low level moisture in southeast West Virginia along with a
weak short wave so some upslope clouds expected. Short wave
tracking through the upper northeast trough on Thursday night
and early Friday morning will provide some lift. But by Friday
morning the 850MB winds forecast to be from the north which is
not as favorable for upslope. Slightly cooler temperatures at
500 MB will result in larger lapse rates and instability
Friday. NAM and GFS showing an increasing amount of moisture
below 700MB Friday night and Saturday and a wedge develops and
strengthens. Have lowered minimum temperatures on Thursday
night, trending closer to MET guidance.


As of 1230 PM EDT Wednesday...

For Monday models continued to show separation between a
northern stream system approaching the Ohio Valley and the
tropical system over the Lower Mississippi Valley. Short wave in
the southwest flow over the Mid Atlantic region forecast to
cross through the area on Tuesday. Confidence in the synoptic
scale weather pattern decreases on Tuesday and Wednesday mainly
due to uncertainty and spread in the guidance with the evolution
of the Gulf of Mexico and southeast coast tropical systems.

Surface high pressure moves into southeast Canada with a strong
wedge down the east side of the Appalachians by Sunday. Cool air
comes down with the wedge by Sunday with 850MB temperatures on
Monday and Tuesday in the +8 to +12 range. Models showing
abundant low level moisture, especially in the foothills and
eastern upslope areas through Sunday. Will cut back the
probability of precipitation on Monday but will leave in
clouds. Plan to slightly lower maximum temperates Sunday
through Tuesday.


As of 706 PM EDT Wednesday...

VFR conditions to be the rule for much of the TAF period,
outside of river valley fog. Skies should generally go SKC from
the Blue Ridge foothills westward with sunset. Indication from
forecast RH profiles tonight towards Lynchburg and Danville of
potential SCT-BKN VFR cloudiness. Northerly winds under 5 kts
will also mitigate any overnight fog for these areas. Best
chance at IFR to LIFR fog is at Lewisburg and Blacksburg where
skies will be clearest and winds the lightest along with
proximity to the Greenbrier and New Rivers.

Areas along the southern Blue Ridge foothills into
Southside/Danville may see lingering VFR stratus deck into the
mid to late morning hours. Should see FEW-SCT VFR fair weather
cumulus otherwise through the TAF valid period. Winds northerly
4-6 kts.

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

Extended Aviation Discussion...

Generally VFR conditions are expected Thursday night into the
weekend as high pressure builds over the region. There will also
be a diurnal trend for late night fog/stratus especially west
of the Blue Ridge with KLWB and KBCB the most likely TAF sites
to be affected. Isolated convection may be possible across the
mountains Saturday into Monday.


As of 1205 PM EDT Wednesday...

KFCX doppler radar has completed all repairs and is now back in




EQUIPMENT...KK is the U.S. government's official web portal to all federal, state and local government web resources and services.