790
FXUS62 KGSP 131026
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
626 AM EDT Tue Aug 13 2024

.SYNOPSIS...
Dry high pressure gradually builds in from the north through
Thursday, pushing a stalled front further south of the area. The
high will drift east off the East Coast Friday, as a cold front
approaches from the west over the weekend. The front will bring
a return of better chances of shower and thunderstorms.

&&

.NEAR TERM /THROUGH TONIGHT/...
     Key Messages...

1) Scattered Morning Showers with Isolated Thunderstorms Possible
Along and East of the Blue Ridge

2) Isolated Strong to Severe Storms Possible this Afternoon and
Early Evening

3) Cooler Temperatures Expected Today

As of 620 AM EDT Tuesday: Main change needed was the increasing of
PoPs over the next few hours due to KGSP radar trends since the
previous update. A broken line of convection developed over the last
few hours along and east of the Blue Ridge Escarpment and has been
wandering east. Have only seen isolated cloud to ground lightning
within this activity in the SC Upstate so far this morning. Areas
west of the Blue Ridge will continue to see dry conditions through
the morning hours. Since cloud cover has increased across the area
temps this morning are running a few degrees above climo. Cloud
cover has limited mountain valley fog formation so far but patchy
fog could still develop around daybreak.

Otherwise, upper troughing will remain over the Carolinas through
the near term while periodic shortwaves track over the region from
the northwest. Meanwhile at the sfc, the southern periphery of
surface high pressure centered over the Great Lakes region will
extend into the Carolinas while a front stalls over the Southeast.
This will lead to a more convectively active day compared to
yesterday. 00z CAMs show scattered convection firing over the
mountains by the early afternoon hours, gradually spreading east
through rest of the afternoon and early evening hours. Although deep
shear will range from 35-45 kts, 00Z HREF ensemble probability shows
less than 2,000 J/kg of CAPE across the forecast area through the
period. However, the 00Z CAMs show the potential for 1200-1500 J/kg
of CAPE across the southern zones during peak heating. The SPC Day 1
Severe Wx Outlook shows a Marginal Risk for isolated severe storms
across the eastern SC Upstate and the southern NC Piedmont (south of
CLT) today. This looks reasonable as the far southeastern zones have
the best chance to see cloud cover breakup briefly this afternoon,
allowing for better destabilization. Damaging wind gusts will be the
main concern with any severe storms that develop. The excessive
rainfall threat will remain isolated with higher shear values in
place allowing for faster storm motion. However, flash flood
guidance continues to be on the low side (mainly across the eastern
two-thirds of the CWA) due to the rainfall from Debby last week and
the recent rainfall over the weekend. Convection should gradually
end from west to east late this afternoon into this evening, with
drier conditions moving in tonight. Temperatures this afternoon will
be much cooler compared to yesterday. However, highs will remain a
few degrees above climo across the Little TN Valley and the Upper
Savannah River Valley. Highs elsewhere should end up a few to
several degrees below climo thanks to higher cloud cover. Lows
tonight will end up near climo to a few degrees above climo. Patchy
fog may develop across the NC mountains and Foothills overnight into
daybreak Wednesday.

&&

.SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
As of 145 AM EDT Tuesday: The short term looks fairly quiet, as the
axis of a deep upper trough will swing east off the East Coast,
and upper ridging builds in from the Lower Mississippi Valley
Wednesday thru Thursday. At the sfc, dry air will filter in from
the north, limiting instability. A light easterly or southeasterly
low-level flow may be enough to force a few isolated showers and
perhaps a garden-variety tstm or two Wednesday and Thursday aftns
in the mountains, but otherwise, it should be partly cloudy with
temps slightly below normal. Highs in the mountain valleys and
Piedmont will be mainly in the low to mid 80s and lows in the mid
to upper 60s.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
As of 230 AM Tuesday...The medium range guidance is in good
agreement on a vigorous shortwave diving thru the western Great
Lakes Friday, carving out a fairly deep upper trough across the
Ohio Valley Saturday, then persisting as a long wave trough across
the eastern CONUS into early next week. An associated low pressure
system will bring a cold front into the Ohio Valley and possibly
crossing the forecast area over the weekend. The front is expected
to stall out roughly across the Midlands or Coastal Plain Sunday or
Monday. Overall, the front will have limited moisture to work with,
but should support scattered to numerous showers and thunderstorms
in the NC mountains with help of NWLY upslope flow Friday and
Saturday. Downsloping east of the mountains may limit coverage,
but support a return of near-normal to slightly above-normal
temps. Drier air filters in behind the front Sunday into Monday,
lowering PoPs and bringing temps down a couple degrees.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
     Key Messages...

1) Scattered Morning Showers with Isolated Thunderstorms Possible
for TAF Sites East of the Mountains

2) Scattered Showers and Thunderstorms Return this Afternoon for All
Terminals

3) Generally MVFR/VFR Conditions Expected for Most Terminals

At KCLT and elsewhere: 12Z TAF period will remain fairly active at
least through today. A broken line of showers has develop along and
east of the western North Carolina mountains this morning and
continues pushing east. Have TEMPOs for -SHRA for all terminals east
of the mountains through the morning hours. KAVL will most likely
stay dry through the morning hours but have a TEMPO for MVFR cigs
and fog around daybreak. KHKY could see IFR cigs develop by mid-
morning so have this accounted for in a TEMPO. Elsewhere generally
MVFR to VFR cigs and vsbys are expected through the period.
Scattered showers and thunderstorms are expected to develop this
afternoon and evening so have TEMPOs for -TSRA at all terminals to
account for this activity. Wind direction will remain N/NE east of
the mountains through the TAF period. Winds at KAVL will be calm to
light NW through daybreak before turning more E/NE. KAVL will likely
see light and VRB winds tonight as well as the potential for patchy
fog. Patchy fog may reach KHKY but confidence on this is low for
now. Drier conditions will filter into the region from west to east
later this afternoon into this evening, continuing into Wednesday
morning.

Outlook: Expect mostly diurnal isolated to scattered diurnal
convection through Thursday. Coverage of convection increases Friday
into Saturday as a cold front approaches out of the west. Patchy fog
and low stratus will be possible each night in the mountain valleys
and in any locations that received heavy rainfall the day prior.

&&

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

&&

$$

SYNOPSIS...ARK
NEAR TERM...AR
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...AR