Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 192336
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
736 PM EDT Sat Aug 19 2017

.SYNOPSIS...
A front will remain stalled over the eastern Carolinas tonight into
Sunday before dissipating. High pressure works in from the Ohio
Valley during the weekend, then overhead Monday resulting in
mainly dry weather across the region. Another cold front will
approach the area by the middle of next week with the next
chance for showers and storms.

&&

.NEAR TERM /THROUGH SUNDAY/...
As of 736 PM EDT Saturday...Per water vapor trends, mid/upper-
level trough axis now appears to be clearing our far
southwestern counties; this feature lying atop weak surface
ridge building in from the west. Through next several hours,
trend will be for dissipating fair weather cumulus along with
generally clear skies. There may be some convective debris high
clouds that approach our northern and northwestern counties
later in the overnight from convection across PA, northern WV
and into southeast OH, convection that should remain north or
northwest of the forecast area. Look for good radiational
cooling and drying through tonight. Should see nocturnal patchy
radiation fog develop later in the overnight in and adjacent to
the Greenbrier, New and Holston/Clinch river valleys. Lower
confidence on dense fog in these areas due to expected dry
advection overnight, but vis could be as low as one mile at
times. All in all though, a fairly comfortable mid- August
evening, even in southeastern counties as dewpoints start to
drop to more comfortable levels. Lows appear on track with no
other changes needed attm.

Previous near-term discussion issued at 230 PM follows...

Upper trough will pass across the region this evening followed by
flat ridging overnight into Sunday. Most moisture remains to the
north closer to the cool pool aloft, so keeping things dry this
evening per latest model consensus. Next round of weak cool
advection to follow this impulse overnight as weak surface high
pressure builds in from the northwest under increasing subsidence.
However may see some lingering strato-cu/mid deck in the wake of the
trough this evening before clearing overnight. Otherwise expect
somewhat lower dewpoints under mostly clear skies late to allow for
more comfortable lows in the 60s, with perhaps a few 50s valleys.
Appears some patchy fog again possible late tonight espcly valleys
although should be less than last night per drying from this
afternoon.

High pressure remains just north on Sunday with a gradual transition
to low level southeast flow espcly southern/east sections in the
afternoon. Models attempt to nudge a bit more low level moisture up
against the southern Blue Ridge late where instability appears
highest. A few solutions even hinting at the potential for isolated
convection far southwest ridges late but looks overdone per dryness
aloft off forecast soundings. Thus leaving out any pop mention with
overall mostly sunny skies for now. Given little temp change aloft
and the flow turning more southerly, bumped highs up a bit more but
not as warm as the latest Met mos which pushes mid 90s southeast.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
As of 240 PM EDT Saturday...

High pressure will be centered along the Appalachian Sunday night,
then drifts off the VA/NC coast on Monday. With some weak southerly
upslope flow and marine moisture, scattered showers and
thunderstorms are possible along the Blue Ridge Monday afternoon.
Any afternoon storms will then drift east in zonal flow and fade
over the foothills during the evening. Cloud cover Monday afternoon
should not be enough to hamper viewing of the eclipse. The eclipse,
coming over the region during peak heating, may hamper afternoon
convection to isolated coverage. Temperatures during the eclipse may
drop 3F to 5F, especially south of a line from Richlands VA to Mount
Airy NC. Temperatures will rebound following the eclipse with
daytime highs ranging in the 80s with near 90F across Southside.

High pressure will lose its hold on the region as a cold front
approaches from the west Tuesday. Models have backed off on diurnal
afternoon convection Tuesday, likely due to the lack of jet dynamics
and increasing heights aloft. Some prefrontal showers may enter SE
WV mountains late in the day, however confidence is low. Since we
are expecting more sun and less rain, temperatures will warm above
normal with 80s across the mountains and lower 90s east.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
As of 255 PM EDT Saturday...

Despite a very warm environment across the region, models are
pushing a cold front across the area on Wednesday. Most models are
running fast and actually have the front coming across SE WV during
the early morning hours Wednesday. Both the GFS and ECM have the
front hung across the mountains Wednesday morning then jumping it to
the piedmont in the afternoon. This may leave a minimum or shadow of
rainfall along the Blue Ridge and foothills. The best low level jet
is north towards DC and with the winds coming around to the west
quickly, the severe threat will be limited. The exception to the
rule will be across NW NC piedmont and Southside VA late in the
afternoon and into the evening, where instabilities will be high.

Following the front Wednesday night, cooler drier air will move into
the region and remain into next weekend. Temperatures will likely be
cooler than normal by 5F or so. Humidity levels will also be
comfortable as dew points drop into the 50s

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 736 PM EDT Saturday...

VFR through the period outside of potential LIFR river valley
fog at Lewisburg and MVFR patchy fog at Blacksburg. Surface high
should continue to build in from the west through overnight.
Could see some convective debris high clouds filter in from the
northwest but inconsequential. Should see good radiational
cooling tonight which should lead to fog tonight at Lewisburg
and Blacksburg. Fog may also be possible at Lynchburg but
confidence is lower. Light southwest winds should become light
to calm overnight.

Any fog burns off to VFR conditions on Sunday. Some guidance
generates some showers or thunderstorms along the Blue Ridge
tomorrow afternoon, but this probably is overdone by the extent
of dry air in mid-levels that should mitigate development. Left
out mention in the TAFs attm. Light south winds expected Sunday.

Extended Aviation Discussion...

Moisture will gradually start to return early next week as high
pressure weakens and moves offshore ahead of another cold front
that should arrive from the northwest around midweek. However
still appears should remain mainly VFR Monday into Tuesday with
localized MVFR under isolated to widely scattered convection.
Late night/early morning fog will also be possible each day.
Better potential for sub- VFR will come Wednesday when possibly
more widespread showers and storms arrive with the next cold
front.

&&

.EQUIPMENT...
As of 400 AM EDT Friday Aug 18th...

KFCX doppler radar expected to be down for the rest of the
month due to a failing bull gear. Technicians are working on the
radar, through next week and the radar will most likely stay
down completely as the repairs are being made.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...JH
NEAR TERM...AL/JH
SHORT TERM...RCS
LONG TERM...RCS
AVIATION...JH
EQUIPMENT...RAB/WERT/WP



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