-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 161727
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
127 PM EDT Wed Aug 16 2017

.SYNOPSIS...
Weak high pressure over our area will be sandwiched between a
front over the mid-Atlantic and a trough off the southeast
coast. This pattern stays the same into Thursday, before a cold
front shifts from the western Ohio Valley into our area Friday.
This cold front will slide into the Carolinas during the
weekend.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 125 PM EDT Wednesday...Earlier fog has since fully burned
off, and in its place has been cumulus clouds with insolational
heating. Deepest cumulus per visible imagery in far southwest VA
in Smyth, Wythe and Tazewell counties, and in the mountains of
NC. Regional radar shows scattered showers starting to develop
north of Abingdon and Bristol that should brush across those
aforementioned counties this afternoon associated with weak
surface low and associated weak disturbance aloft. A few
thunderstorms possible, with brief downpours in these as well,
but not expecting storms to become overly strong at this point
with SBCAPE values presently at/below 1000 J/kg per SPC
mesoanalysis. Current forecast reflects this pretty well with
no significant changes needed. Other than accounting for current
T/Td observational data and blending in with current forecast,
no other alterations were made attm.

Previous near-term discussion issued at 236 AM follows...

Overall airmass does not change much this period. Will see deeper
moisture/higher pwats to our south while a frontal boundary stays
draped across the mid-Atlantic into the midwest, with Hurricane Gert
veering out to sea.

This morning will be concentrating on fog, as some areas have dropped
to under 1sm, but overall still not seeing enough coverage for a
dense fog advisory as rainfall yesterday was less numerous than
expected. Will monitor conditions and issue a Special Weather
Statement at least to cover the patchy dense fog, and possibly
upgrade to a Dense Fog Advisory if it becomes more widespread.

Once fog lifts there should be a period of mainly sunshine though
some higher clouds will stream by in the westerly flow aloft. Will
see the fog turn into a cu field then some towering cu to CBs after
midday in the southwest mountains of VA into NC, as weak upper
disturbance and moisture convergence along the spine of the
Appalachians acts to form showers and storms. Coverage today will be
low, with most not seeing any rain.

With more sunshine will see warmer temperatures with highs in the
80s, around 80 NC mountains, higher ridges of WV/VA to upper 80s
east of the Blue Ridge and including Roanoke, Lexington, VA.

Tonight, the upper heights rise with weak ridging. Still models
showing weak convergence into the overnight across the southeast,
then another area of lift reaches the central Appalachians by dawn.
Very low confidence on much shower coverage overnight, after evening
showers/isolated storms fade over the NC foothills and piedmont.
Added a slight chance of showers around dawn in the WV mountains as
well. Fog will form in the river valleys as well late tonight but
increased cloud cover appears to limit coverage. Lows staying above
normal with mid to upper 60s mountains, to lower 70s out east.
-- End Changed Discussion --

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 300 AM EDT Wednesday...

Weak ridging aloft will continue Thursday as a weak warm front aloft
slides back through the area from the southwest. A low level
southwest flow will advect deeper moisture north Thursday afternoon.
The combination of a boundary, low level convergence and stronger
instability will result in scattered showers and thunderstorms. The
Day Two Convective outlook keeps our area in general thunderstorms
with marginal risk to our west across the Ohio Valley. High
temperatures Thursday will range from the mid 70s in the mountains
to around 90 degrees in the piedmont.

A few showers and thunderstorms may linger into Thursday evening
before loss of heating and exodus of the weak boundary takes place
Thursday night. Low temperatures Thursday night will vary from the
mid 60s in the mountains to the lower 70s in the piedmont.

A cold front should slowly pivot toward the region Friday afternoon
preceded by a lead band of showers that could jump into the eastern
lee trough during the afternoon where deeper convection possible.
Weak lift is expected ahead of the boundary, given that most upper
support shearing out to the northeast with the passing weak
shortwave. Behind the pre-frontal axis, a west winds may hinder
convection in the mountains. However progged instability still quite
strong east of the mountains and if timing is slower then could see
better thunderstorm coverage in the east. There is enough shear,
better instabilities and healthy lift to support isolated strong
storms. High temperatures Friday will generally be from around 80
degrees in the west to near 90 degrees in the east. Temperatures
will depend on cloud cover and timing of convection.

Any convection Friday evening will taper off with the loss of solar
heating Friday night. Low temperatures Friday night will feature
readings from the upper 50s in the mountains to the lower 70s in the
piedmont.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 300 AM EDT Wednesday...

Transition to more of an upper troughing regime will again occur
over the weekend allowing another surface cold front to push into
and perhaps south of the region by early next week. Latest models
again have differences on the southward push of drier air behind the
front espcly given another upper disturbance that looks to pass just
north by later Sunday. However appears passage of this feature may
be enough to briefly shunt deeper moisture to the south/east before
the trough flattens into broad ridging early next week. Therefore
will leave in some low pops mainly southeast third later Saturday
where the front may slow up during heating, and slight to low end
chance pops espcly southern/southwest sections Sunday as the
wave/trough passes. Monday look drier but rather hot with surface
high pressure building in from the north behind the front resulting
in better subsidence under a weak wedge. Thus limiting any pops to
start the week to mainly the southern Blue Ridge, with overall more
sunshine elsewhere for now. Added some light pops to Tuesday and
Wednesday as weak shortwaves rotate through. Confidence is low on
shortwave energy in the extended that may rotate further north
around the subtropical ridge as hinted at by ECMWF.

Despite the frontal passage, will actually see warmer high temps
given heating of somewhat drier air and warming aloft to start next
week. This supports overall above normal highs with low/mid 80s
mountains to near 90 east through much of the period.

&&

.AVIATION /17Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --
As of 125 PM EDT Wednesday...

VFR conditions through much of tonight across the terminals
tonight. Some potential for an isolated to widely scattered
shower or thunderstorm affecting far southern VA into the
southern Blue Ridge in NC. Indicated VCSH at Bluefield, which
would be the northeastern extent of this threat this afternoon,
but more of an awareness for routes through the southern Blue
Ridge toward TN. Any showers or storms should dissipate and/or
pivot into the central NC Piedmont by 04z. However, through
mid-evening there should be a considerable degree of VFR low to
mid clouds associated with southwesterly moisture advection.
This lends uncertainty on the extent of radiation fog after 06z,
even in the more customarily fog-prone river valleys. Indicated
BR in at Lewisburg, but only at 5 SM as confidence is on the low
side. Should fog develop, it would in all likelihood not be as
dense or extensive as observed earlier this morning. Winds light
west to southwest becoming light and variable by morning.

Multi-layered VFR cloudiness expected Thursday. With humid
dewpoints, air mass tomorrow is only weakly capped to
convection, so any breaks in the cloudiness should produce at
least scattered showers as early as mid-morning. Thunderstorms
becoming more likely after 16z Friday. Couldn`t rule out this
threat anywhere, but a somewhat more favorable area would be
within a few miles either side of the Blue Ridge. While strong
storms are not anticipated before 18z, a few will produce
lightning and short- duration MVFR to LIFR visibility
restrictions in heavy rain. Indicated VCSH prior to 16z, with
VCTS indicated after 17z to reflect potential thunderstorms in
vicinity of TAFs. Winds southeast to south 4-6 kts, though may
tend southwest at Bluefield.


Extended Aviation Discussion...

Expect a continued increase in shower/thunderstorm coverage
and strength after 18z Thursday, lasting until 03z Friday.
Outside of thunderstorms look for VFR conditions. Overnight fog
is a possibility in the river valleys and in areas that do see
rain, though cloud cover/convective debris may limit its spatial
extent.

Another round of scattered afternoon showers and thunderstorms
Friday associated with the primary cold front, though VFR
prevails outside of showers or storms. 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.
-- End Changed Discussion --

&&

.EQUIPMENT...
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.

&&

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

&&

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