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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KRNK 160100
AFDRNK

Area Forecast Discussion
National Weather Service Blacksburg VA
900 PM EDT Wed Aug 15 2018

.SYNOPSIS...
High pressure will bring overall fair weather to the
Appalachians and central mid Atlantic region tonight. This high
will then slide off to our east tomorrow and bring a chance for
showers and thunderstorms back to the forecast. Low pressure
over the Great Lakes will track east Friday and Saturday pushing
a cold front into the mid Atlantic region, with a good chance
for showers and thunderstorms through the weekend and into the
first part of next week.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 845 PM EDT Wednesday...

Spotty light showers just west of the region continue to fade
this evening upon moving into weak ridging aloft and subsequent
mid level dry air seen on evening raobs. Latest analysis also
showing little in the way of instability so expect any residual
light showers to fade later this evening as well as upstream
convection that may approach late. However degree of high/mid
clouds remains iffy overnight with swath of debris clouds likely
to linger over the next few hours. This may limit fog formation
at least early on so removed most mention until after midnight
when expect some decrease in cloudiness. Also with dewpoints up
slightly espcly east, bumped up lows a bit and if clouds linger
over the west then may need to increase even more later on.
Otherwise planning to stay dry overnight under partly cloudy
skies west to mainly clear east, with lows ranging from the low
60s mountains to upper mid/upper 60s elsewhere.


Previous discussion as of 245 PM EDT Wednesday...

Radar is essentially devoid of returns early this afternoon but
visible satellite imagery shows some good Cu towers as an
approaching short wave works on some surface instability with
marginal lapse rates aloft. Thus, expect a slight chance for
widely scattered/isolated showers/thunder along and west of the
Blue Ridge, primarily the southern Blue Ridge into the
mountains of NC before any convective elements dissipate this
early evening.

Expect mid/high clouds upstream to move over the region tonight,
but there are indications the clouds will be breaking up a bit
as they go. With this in mind, will go a bit below guidance as
expect there will be a few windows for radiational cooling to
occur. This should also result in another round of valley fog
west of the Blue Ridge tonight. Lows tonight look to be in the
mid/upper 60s east of the Blue Ridge with upper 50s/around 60 to
the west along with some cooler readings in the valleys. If
clouds come in thicker than anticipated, will have to revisit
the temperature and fog forecast.

Surface high pressure will be drifting off to the east
tomorrow, allowing for southwesterly return flow to develop. The
best isentropic lift will follow the strongest 850mb winds up
into the Ohio valley to our west, but there looks to be enough
forcing for some scattered/widely scattered showers/thunder
mainly along and west of the Ridge again tomorrow afternoon.
Highs tomorrow will be a bit warmer with lower 90s east of the
Ridge, mid/upper 80s to the west.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 300 PM EDT Wednesday...

Fairly typical summertime pattern with weak flow aloft at the
southern and central latitudes of the CONUS and stronger activity
along and north of the Canadian border. Global models in general
agreement however in trying to reestablish troughing in the eastern
half of the CONUS as the subtropical ridge expands somewhat across
the desert southwest. This will allow for increasing southwest flow
aloft, increasing humidity and higher chances for mainly
afternoon/evening convection both Friday and Saturday, The best
chances for showers and thunderstorms will be in the west closer to
the best upper support and deeper moisture but mesoscale
interactions likely to support scattered storms elsewhere as well.
Daytime high temps will be moderated by considerable cloudiness
while reverse process in effect during the overnight yielding
generally above normal lows. Humidity will again become more
noticeable with dewpoints ranging from the mid-60s northwest to low
70s southeast.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 300 PM EDT Wednesday...

Short-wave ridging or least zonal flow builds in for later Sunday
into Monday as the first trough lifts out. Precipitation chances
will decline somewhat Sunday and Monday but cannot remove pops
entirely under a still moist and conditionally unstable air mass.
Yet another trough is forecast to develop over the central U.S.
early next week. This will be fairly amplified for what is still mid-
summer, especially as advertised by the 12z ECMWF and CMC which spin
up a fairly strong surface low (sub-1000 mb) for the season over the
mid- to upper Mississippi Valley late Monday into Tuesday. This
feature lifts north into the Great Lakes by Wednesday with a
potentially broad shield of precipitation along and ahead of a
frontal boundary over the central states and moving into parts of
the Ohio valley and the western portions of our CWA Tue/Wed. GFS is
considerably less aggressive with this feature but general pattern
is similar. Either way precipitation chances will be on the increase
early to mid-week. Little significant change in temperatures
expected with no significant heat but plenty of humidity and fairly
warm overnight temperatures owing to high moisture and clouds.

&&

.AVIATION /01Z THURSDAY THROUGH MONDAY/...
As of 655 PM EDT Wednesday...

Still looking at mainly VFR this evening with mainly some
passing mid/high clouds after late afternoon cumulus fade. Main
uncertainty is with the extent of these mid clouds overnight and
the affect on radiational cooling that could lead to fog
formation espcly in the valleys. Models continue to hint at some
fog over the west late but probabilities remain low of seeing
widespread fog/stratus given so much debris cloud around at
least early on. Thus plan to back off low vsbys a bit but still
appears a brief period of at least IFR vsbys/cigs possible at
KLWB and KBCB with MVFR at KDAN toward daybreak. Any fog/stratus
will burn off Thursday morning with VFR expected all sites into
the afternoon. Widely scattered showers/thunder may develop
Thursday afternoon but given better forcing to the west through
most of the valid period wont include any mention at the TAF
locations at this point.

Winds will generally be light tonight before turning southwest
at 5-10 knots Thursday afternoon.

Continued medium confidence in sub-VFR tonight. High confidence
other parameters through Thursday.


Extended Discussion...

Scattered afternoon and evening showers and storms will be
possible at airports west of the Blue Ridge Thursday night.
The next cold front and chance for more widespread showers and
thunderstorms with associated MVFR conditions arrives on Friday
and will keep chances of showers and thunderstorms through
Monday.

&&

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

&&

$$
SYNOPSIS...AMS
NEAR TERM...JH/MBS
SHORT TERM...PC
LONG TERM...PC
AVIATION...AMS/JH/MBS