Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 180130

Area Forecast Discussion
National Weather Service Blacksburg VA
930 PM EDT Thu Aug 17 2017

Warm, muggy conditions to continue tonight and into part of Friday
ahead of a cold front. Scattered to numerous showers with scattered
thunderstorms continue late this afternoon into early this evening.
A few storms may produce localized downpours along with gusty winds.
Another opportunity for scattered showers and thunderstorms, a
couple of which may be strong east of the Blue Ridge. Still
rather warm into the weekend, but with slightly less humidity.


As of 930 PM EDT Thursday...

Diurnally biased convection has dwindled to a few isolated cells
mainly north of Interstate 64, with another area of light rain
from dissipating thunderstorms in the foothills of NC. Expect
just a few lingering showers overnight with some clearing giving
way to patchy fog once again. Another muggy night with low/mid
70s east of the Blue Ridge to mid/upper 60s west with some
cooler readings in the valleys.

Previous discussion...

Leftover showers and storms could linger early tonight into the
NC Piedmont/Southside VA. Should see brief clearing from the
Blue Ridge west, and given background humid air mass that could
lead to a good coverage of patchy fog. Eastern and southern
counties may struggle to fully shake free of clouds overnight
with patchy fog mainly in cloud breaks here, while enough
southwest wind flow across the Mtn Empire and southeast WV to
limit fog coverage. Warm, muggy lows from the upper 60s to mid

Friday: Should have a good amount of early-day cloud cover in place
east of the Blue Ridge, ahead of the primary cold front which 12z
NAM/GFS progs to be near our western doorstep by sunrise. This is
maybe a little sooner than recent guidance had indicated. Question
for Friday is on convective coverage and strength given the earlier
frontal timing and potential for morning cloudiness to slow
destabilization in the east. Should have more limited chances for
thunderstorms west of I-81 perhaps as soon as mid to late morning,
but with an increasing trend as the front makes its eastward
advance. The better chance for strong to localized severe storms is
to the northeast in northern VA where deeper shear and strongest
lift is located, but a corridor of stronger storms could exist from
Amherst County to Surry County eastward. Heavy downpours certainly
possible along with localized gusty winds in strongest cells. Front
should be clearing the forecast area by mid to late afternoon, with
notably drier air filtering in on northwest flow. Until then, expect
another warm and muggy day in the Piedmont (heat index values 95-
98). Earlier timing of frontal passage leads to lower highs in the
upper 70s/lower 80s from I-81 westward, with highs mid/upper 80s
east, though a few potential low 90s in the central VA/upper NC


As of 331 PM EDT Thursday...

Cold front will cross east of the area Friday night taking most showers
out of the region by late evening if not sooner as evidenced by progged
lowering 850 mb moisture/theta-e early on. Thus only leaving in some
low chance pops east of the Blue Ridge during the evening before
clearing overnight. Also may see a few upslope induced showers far west
behind the front but should be quite isolated with only a brief mention
needed. Lows mostly 60s except lingering muggy low 70s southeast.

Boundary will briefly stall just to the southeast Saturday
ahead of a rather strong trailing upstream shortwave trough that will
pivot across Saturday afternoon. This may cause some backing of the
flow including a bit of a northward jog in moisture before better
subsidence arrives behind this passing wave Saturday night. Given
rather dry forecast soundings and weak northwest flow, appears can
leave out pop mention for now, with mainly just scattered cumulus

Upper flow will then flatten under slowly building heights on Sunday
with surface high pressure building in from the northwest. Forecast
profiles again indicate quite a bit of dry air aloft that should again
limit shower chances. However with moisture nearby to the south and the
low level flow turning more southeast in the afternoon, cant totally
rule out isolated convection across the far south or southwest where
guidance shows some return instability into Sunday evening. Otherwise
partly to mostly sunny at this point.

Will remain quite warm/hot through the weekend given little change in
temps aloft behind the front and weak downslope flow until late Sunday.
Should be a little less humid Saturday before becoming muggy again
later Sunday with highs both days in the 80s mountains to lower 90s


As of 331 PM EDT Thursday...

Flat upper ridging will remain in place to start next week as surface
high pressure shifts from the Mid Atlantic on Monday to off the
southeast coast by midweek. This along with warming aloft within a west
to southwest trajectory should keep things quite warm and increasingly
humid from later Monday into Wednesday. Convective chances early on
appear iffy with only faint forcing later Monday when higher PWATS
begin to advect back north, followed by gradual height falls on Tuesday
when deeper moisture will be somewhat back in place. Most guidance
showing only isolated showers/storms mainly south/east late Monday with
perhaps a scattering of storms Tuesday espcly where aided by
orographics. Highs likely around 90 east Monday/Tuesday and 80s
elsewhere except possibly a little lower Tuesday far west pending

500 mb pattern will once again become more amplified as another upper
low crossing north of the Great Lakes helps dig out an even deeper
eastern trough by the end of the period. This feature will also propel
a strong cold front toward the area Wednesday with the boundary likely
just south of the region during Thursday. Lead pre-frontal trough axis
likely to spark better coverage of showers/storms Wednesday
afternoon/evening, followed by cooler/drier air during Thursday.
Therefore will include higher chance to low likely pops Wednesday and
then mostly residual showers southern sections Thursday pending timing
of the frontal exodus by then. Should see some cooling due to clouds
including more showers Wednesday, then cool advection behind the front
resulting in highs only 70s mountains to mid 80s east Thursday.


As of 800 PM EDT Thursday...

Somewhat complicated forecast through the period due to pre-
frontal trough and associated convection moving through the
forecast area now, and a new frontal system moving into the area
from the west Friday. Would expect scattered convection to
continue through about 02Z before generally dissipating.
However, may not see all activity diminish due to very moist and
warm/unstable air mass in place. Dissipating convection may
reach western areas toward daybreak. Mostly VFR ceilings
through the evening, outside MVFR ceilings in TSRA/SHRA
activity. Overnight, with moist ground and late day rainfall in
many spots, look for patchy dense fog, mainly impacting BCB and
LWB, with patchy MVFR fog at other locations throughout the late
night and early morning hours. A period of IFR-LIFR conditions
are possible at BCB and LWB in particular, with MVFR elsewhere.

Expect convection to redevelop and increase along the new
frontal boundary as it moves through the CWA Friday. Best chance
for widespread stronger convection will be across the Piedmont.
Widespread MVFR ceilings are expected west of the Blue Ridge
during the morning, with mostly VFR ceilings elsewhere outside
of SHRA/TSRA activity.

Winds will be mostly light and variable overnight, becoming
WSW-W 4-8kts after daybreak Friday, with low end gusts at BLF
during the afternoon.

Medium confidence in ceilings throughout the TAF valid period.
Medium confidence in visibilities throughout the TAF valid
Low confidence in thunderstorm potential throughout the TAF
valid period.
Medium to high confidence in wind speed and direction throughout
the TAF valid period.

Extended Aviation Discussion...

Weak high pressure will build into the area Saturday. Dry
advection and light to moderate west to northwest winds behind
the front Friday night could keep overnight fog coverage
limited, but a potential sub- VFR ceiling is possible at
Lewisburg and Bluefield.

Mainly VFR conditions for the weekend under weak high pressure.
Scattered thunderstorms and periods of MVFR conditions return
next week, with late night/early morning fog possible almost any


As of 755 PM EDT Saturday Aug 12th...

KFCX doppler radar will continue to be down for the rest of the
month due to a failing bull gear. It will only be operational
during this time frame for brief periods if an imminent
significant widespread severe weather and/or hydrologic event
occurs. Operating the system for any amount of time until the
bull gear is replaced risks a catastrophic failure that would
further extend system downtime. From the 17th through the 27th
the radar will most likely be down completely as the repairs
are expected to be made during this period.




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