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957
FXUS62 KGSP 160235
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1035 PM EDT Wed Aug 15 2018

.SYNOPSIS...
A trough of low pressure will develop west of the Appalachians
through Thursday and then persist well into the weekend as a stalled
surface front lingers north of the region. Moisture will increase
ahead of this system to produce a lengthy period of unsettled
weather from Friday onward. A weak cold front will approach slowly
from the northwest early next week and likely arrive in the region
on Wednesday.

&&

.NEAR TERM /THROUGH THURSDAY/...
As of 1030 pm: Another quiet/seasonably mild night is in store, with
fog and low stratus likely developing again in the mtn valleys
during the early morning hours. However, in light of the lingering
mid and high-level clouds seen across the area this evening, it may
take a couple of more hours before the fog/stratus begins to expand.
Min temps should be right around normal.

An upstream trough will amplify over the Midwest on Thursday, but
any shortwaves ejecting east from this system should impact mainly
the Ohio Valley and central Appalachians. Once again, the best
forcing over the southern Appalachians will be weak terrain
triggering. Scattered PoPs appear warranted as better moisture
returns in the S to SW 850 mb flow. Temperatures should recover at
least another degree or two despite the clouds given the warm
advection.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
As of 2:30 PM EDT Wednesday: We will allow the pockets of showers
and thunderstorms across our forecast area (FA) Thursday evening, to
wane or end with the loss of heating and minimal forcing. The
exception will be in the mountains where a SW flow will continue to
draw moisture into the western slopes, in a mechanical lift type
fashion.

It is difficult to pick up the various lobes of energy in a seamless
wave train of vort lobes. One appears destined for our area Friday,
while a lee side trough settles in. Precipitable water values should
be rising to between 1.75 and 2.00 inches. SBCape on the order of
1500-2000 J/KG, although 0-6KM bulk shear will remain aob 20 knots.
Overall thinking is for POPS to rise into the likely category west,
and medium chance east. The forecast is for the upper level energy,
interacting with a moist atmosphere and meso convergent areas to
ignite the showers and thunderstorms. The potential for locally
heavy rain and a few downburst episodes not out of the question.

The positive tilted trough approaching will be gradually deamplifying
Friday night and Saturday. Nevertheless, several waves of energy
will continue to work through the SW flow aloft, and the stubborn
surface wind shift/lee side trough will remain in place. Therefore,
although we back off POPS Friday night to some degree, they should
not end. The parade of S/W type features will continue into
Saturday, as a result with instability on the increase once again,
expect even better chances of showers and thunderstorms. We have
POPS Saturday reaching categorical in the mountains and high chance
or low likely values elsewhere.

Note, the idea that the surface front will become nearly stationary,
or waffle north and south beyond this part of the forecast cycle, is
a bit worrisome for heavy rain potential. At least during this part
of the forecast cycle the models are not very interested in heavy
rain.

Temperatures in this part of the forecast will be knocked back from
earlier in the week, with clouds and the precipitation potential.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
As of 2:30 PM EDT Wednesday: Our forecast area (FA) sits under one
trough Saturday night and Sunday. As the lead system pulls out there
should be a lull sometime Sunday morning. However the next upper
level system will be dropping into the Missouri Valley later Sunday,
destined to be a weather player in the extended portion of the
forecast.

With fairly high precipitable water values in place, and the old
frontal boundary draped across our region, scattered to numerous
showers and thunderstorms should erupt Sunday into Sunday evening,
with a bit of a diurnal maximum.

Unlike the earlier trough, this feature approaching early next week,
and into the middle of the week, appears stronger and has more
amplitude associated with it. The quasi stationary boundary may well
be shifted back to the north as the southwest flow increases.
Judging by the jet structure of a favorable right entrance region of
a jet-let, this along with upper level energy support a continuation
of the unsettled weather into midweek.

POPS are quite high during the period, although there will be breaks
or minimums in the long range time period. However, the theme
appears to be sound.

Temperatures will be tricky if we get back into the warm sector, or
clouds thin a bit at times. Persistence in the forecast seems to be
the best route to take at this point.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Very isolated convection, mainly in areas
east of KCLT, will diminish over the next couple of hours.
Otherwise, the main concern for this period will be the potential
for fog/low stratus in the mtn valleys early Thu morning. While KAVL
has largely been spared of restrictions the past couple of mornings,
increasing dewpoints will result in increasing chances for IFR or
lower conditions Thu morning, and 2SM/SCT003 are advertised from
10-13Z. The other main TAF sites should remain VFR. Otherwise,
tomorrow afternoon/evening is expected to be slightly more
convectively active than today, but still not enough to warrant any
Prob30s outside of KAVL. Winds will become calm or light/vrbl this
evening, becoming SW at around 5 kts by late morning/early afternoon
Thu.

Outlook: Increasing coverage of diurnal thunderstorms us expected
from Friday through the upcoming weekend and into early next week.
Restrictions will be limited mainly to areas in heavy showers and
low clouds/fog across the mountain valleys each morning.

Confidence Table...

            02-08Z        08-14Z        14-20Z        20-00Z
KCLT       High 100%     High 100%     High 100%     High 100%
KGSP       High 100%     High 100%     High 100%     High 100%
KAVL       High 100%     Med   62%     High 100%     High 100%
KHKY       High 100%     High 100%     High 100%     High 100%
KGMU       High 100%     High 100%     High 100%     High 100%
KAND       High 100%     High 100%     High 100%     High 100%

The percentage reflects the number of guidance members agreeing
with the scheduled TAF issuance flight rule category. Complete hourly
experimental aviation forecast consistency tables and ensemble forecasts
are available at the following link:

www.weather.gov/gsp/aviation

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.

&&

$$
SYNOPSIS...HG
NEAR TERM...HG/JDL
SHORT TERM...TS
LONG TERM...TS
AVIATION...JDL