FXUS61 KRNK 231838

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

A cold front will continue to move southeast 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.


As of 238 PM EDT Wednesday...

KFCX WSR-88D is back in service !

A cold front with associated showers and thunderstorms will move
southeast this afternoon into tonight. Solar heating has created
some surface based instability ahead of the boundary reinvigorate
convection with the front mainly east of the Blue Ridge mountains.
The northwest winds behind front are hindering showers in the

The best low level winds and dynamic support will be moving by to
our north which will greatly limit the potential for any
thunderstorms to become severe. The Day One Convective Outlook
has most of the forecast area in general thunderstorms, with
marginal risk of severe clipping only portions of extreme
southeast counties.

A large area of high pressure will move out of central Canada and
build eastward behind the front, bringing an end to any lingering
showers early tonight. Slackening winds west of the Blue Ridge and a
cooler airmass should help generate some late night valley fog.
Low temperatures tonight will range from the lower 50s in the
mountains to the mid 60s in the Piedmont.

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 120 PM EDT Wednesday...

MVFR convection associated with cold front moving southeast
across the region this afternoon into tonight. With the front
advancing into the Piedmont during peak heating, expect enough
surface based instability to generate scattered showers and
thunderstorms along it east of the Blue Ridge this afternoon
into this evening.

Conditions improving to VFR behind the front as winds become
northwest. A large high pressure system will move out of
central Canada and build eastward behind the front tonight.
Winds will begin to come around to the northeast east of the
Blue Ridge overnight as the large surface high begins to
translate toward New England.

Enough northeast wind should develop overnight to prevent fog
across the Piedmont, but good radiational cooling and clearing
skies should promote good fog development at LWB and BCB, but
not as much confidence as usual with advection of drier air into
the region. After any morning fog or low clouds, VFR conditions
will prevail Thursday. Any isolated shower may be possible
across the extreme northern portion of forecast area.

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




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