155
FXUS62 KGSP 151402
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1002 AM EDT Thu Aug 15 2024

.SYNOPSIS...
Dry high pressure gradually builds in from the north today,
resulting in isolated afternoon showers in the mountains. The high
will drift off the East Coast Friday as a cold front approaches
from the west this weekend, bringing better coverage of showers
and thunderstorms. Drier conditions will return behind the front
as well as near normal temperatures early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 920 AM EDT Thursday: Still dealing with a patch of showers
over northeast GA this morning, but expect they will diminish with
the diurnal minimum. After that, we await the development of showers
on the ridgetops. The rest of the forecast was in fairly good shape,
altho sky cover had to be bumped up over the western zones.

Otherwise...expect a repeat of yesterday. Clouds will gradually
decrease through the morning hours. Highs today will be similar
to yesterday`s, remaining near climo to a few degrees below
climo. Temperatures will be slightly cooler in the mountains but
slightly warmer east of the mountains this afternoon. 00Z CAMs show
the potential for isolated showers develop once again across the
mountains this afternoon and early evening.  Instability looks
even lower than yesterday, not exceeding 500 J/kg, so did not
go with any mentionable thunder chances. May see a bit more
cloud cover today thanks to sfc winds gradually turning S`ly.
Lows tonight should end up a few degrees above climo area-wide
thanks to some lingering cloud cover. Another round of low stratus
and fog may develop again tonight but guidance keeps it confined
to the mountain valleys for now.

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
As of 230 AM EDT Thursday: An upper trough will dig into the Ohio
Valley Friday thru Saturday, bringing an associated cold front
toward the Southern Appalachians.  An increasing SWLY 850mb
flow ahead of the front will bring moisture to the mountains
and should aid in solid chance PoPs with daytime heating Friday
aftn and evening.  30-40 kt of bulk shear may support some
organized convection upstream, with a marginal risk of severe
storms across the NC mountains. The main threat will likely be
damaging wind gusts. The environment east of the mountains will
remain less unstable, but westerly steering flow may bring some
of the convective activity into the Piedmont (as the 00z HRRR
suggests). Even if that happens, convection should generally weaken
as it tracks east. PWATs increase to 1.75-2.0", so there will be
a threat for locally heavy rainfall.  Highs will be slightly above
normal, especially east of the mountains where there will be less
cloud cover. Lows will be near to slightly above normal.

The front should be pushing into the forecast area (or at least
be close just to the west) on Saturday. The front combined with
mid-level troughing and increasing NWLY flow should result in a
relatively active day convectively. With that said, instability
looks modest, and shear will be marginal.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 240 AM EDT Thursday: The medium range guidance still agrees on
a deep longwave trough setting up roughly along the East Coast. The
00z GFS is in line with the 12z ECMWF and Canadian on a slightly
slower progression, resulting in the cold front lingering across
the eastern part of the CWA on Sunday. The front still over the
Piedmont on Sunday may result in another round of convection,
but any severe threat would probably be confined to the southeast
edge of the forecast area.

On Monday the upper trough axis will be overhead and moist NWLY
flow will support showers and a few storms across the mountains,
but it will be generally dry east.  Dry air finally works in Tuesday
under deep-layer NWLY flow. Models disagree on what happens to the
upper trough Wednesday, with the ECMWF closing off an upper low over
the Northeast, while the GFS digs a much more aggressive trough
into the Great Lakes. The Canadian is in between with a trough
axis still over the forecast area. Despite those differences,
they all generally agree on relatively dry weather continuing on
Wednesday. Temps will be near to slightly below normal.

&&

.AVIATION /14Z THURSDAY THROUGH MONDAY/...
Key Messages:

1) Patchy to Dense Fog and Low Stratus this morning at KHKY and KAVL

2) Isolated Showers will Develop Again Across the Mountains this
Afternoon

3) Mostly MVFR to VFR through the 12Z TAF Period

At KCLT and elsewhere: The 12Z TAF period will be similar to what we
saw yesterday. Fog and low stratus have developed again at KHKY and
KAVL this morning. Have TEMPOs at both sites to account for fog/low
stratus through 14Z. Some patchy fog has developed east of the
mountains but this will not have a major impact on the remaining TAF
sites. It will remain dry east of the mountains again today, with
KAVL having the best potential to see some showers around the
terminal. Held off on a mention for VCSH or -SHRA for now as
confidence is too low on whether activity will develop directly over
or near the terminal. Winds will be calm to light NE east of the
mountains, with calm to light SE winds at KAVL through daybreak.
Winds will remain S/SE at KAVL through the period, with winds east
of the mountains gradually turning S/SE this morning. Another round
of mountain valley fog and low stratus may develop again overnight
into daybreak Friday. Fog and low stratus may reach KHKY but so far
guidance keeps it maintained to the mountains for now.

Outlook: Coverage of convection increases Friday as a cold front
approaches out of the west. The cold front will track over the
forecast area this weekend keeping convection around. Drier
conditions return behind the front early next week. Patchy fog and
low stratus will be possible each morning 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/PM
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...AR