679
FXUS62 KGSP 202355
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
755 PM EDT Fri Sep 20 2024

.SYNOPSIS...
High pressure will linger across the area today, though we could see
some widely scattered showers and storms through this evening.  High
pressure will remain through early next week, with hot temperatures
expected over the weekend, before a wetter pattern arrives after
Tuesday.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 525 PM: No major changes this update. Isolated showers
continue along/east of I-77 in area of higher dewpoints and lower
LCLs/CCLs, but cu development has slowed or ended over areas
further west. Revised PoPs to continue the mention near I-77 thru
mid-evening, but remove any mention toward the west. Made slight
adjustments to T/Td trends this evening but think min temps are
on track.

Still expecting heights to gradually rise through the period as a
ridge extending from an upper anticyclone over Texas nudges into the
region. Weak surface high pressure remains over the area through
the period as well. Expect mostly clear skies overnight as the
afternoon cumulus dissipates through the evening. This combined
with light winds and low level moisture, expect another round of
mountain valley fog, some dense, and patchy dense fog outside of
the mountains. Lows will be up to 5 degrees above normal.

Instability looks to be lower Saturday with warming mid
levels. Still there my be enough to combine with differential
heating for isolated convection along and near the Blue Ridge
during the afternoon, but overall chance is lower. Highs will be
around 5 degrees above normal.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
As of 136 PM EDT Friday: Fairly good agreement on the forecast for
the latter half of the weekend and into Monday.  Subtropical ridging
will build over the southern US and Gulf of Mexico through the
period, sharpening on Monday in response to increased troughiness
over the Continental Divide and points west.  This`ll maintain
mostly dry and suppressed conditions over the area on Sunday, before
a broad and ill-defined baroclinic zone arrives in the Ohio Valley
Monday.  Ripples of shortwave energy aloft will ride up and over the
ridge, lending a little synoptic forcing to anotherwise murky setup.
 So, increasing PoPs are warranted through the end of the period
Monday evening.  Temperatures will likely hit the upper 80s to lower
90s on Sunday, with the highest temperatures to be found across the
Savannah River Valley; on Monday, they`ll fall back into the upper
80s in most locations in response to the weakening ridge and
enhanced cloud cover.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
As of 148 PM EDT Friday: Lower-than-typical confidence as we look
out into the medium range.  Another round of more focused shortwave
energy will arrive on Tuesday, further suppressing the ridge over
the eastern CONUS; it`s unclear, though, how strong this effect will
be.  The latest operational GFS depicts the ridge remaining in
place, if perhaps migrating even farther east and exposing the
Carolinas to better deep-layer SW flow and accompanying moisture
flux.  The most recent two runs of the ECMWF depict a complete
dissolution of the ridge, with a massive upper low developing over
the Mid-Atlantic by Wednesday.  The 12z GDPS, comparatively, depicts
an open trough and associated surface front arriving on Wednesday
and Thursday and scouring out the remnants of the ridge.  The
broader ensemble envelope of solutions clearly favors the more
progressive solutions depicted by the GFS and GDPS, but there`s
around 25% support for a more EC-like upper low solution as well.
That is to say, predictability is fairly low past Tuesday or so, but
most solutions will result in some sort of more active/rainy setup
through the medium range...and the more GFS-like solutions would
even introduce some afternoon instability each day, resulting in at
least some isolated thunder chances!

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
At KCLT and elsewhere: Mostly clear skies and light to calm
winds should permit radiation fog/stratus to develop again
tonight. Crossover temps are however a bit lower compared to Fri
morning, and fewer areas saw shower activity Fri, so extent probably
will not be as great. Saw fit to prevail LIFR for the majority of
the early morning at KAVL; cig likely to be persistent in that time
although vsby may go up/down. Retained TEMPO from previous TAF for
KHKY. Elsewhere mentioned MVFR vsby near daybreak with SCT clouds
at LIFR level. Winds generally should pick up from the S in the
morning although with some variability possible in the first few
hrs of the day, with FEW cu developing at MVFR level then mixing
above 030 by midday. An afternoon SHRA can`t be ruled out at KAVL
but chance far too low to mention.

Outlook: No appreciable return of moisture or precip chances
expected until early to middle of next week. Daybreak restrictions
could recur each morning especially in mountain valleys.

&&

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

&&

$$

SYNOPSIS...MPR
NEAR TERM...RWH/Wimberley
SHORT TERM...MPR
LONG TERM...MPR
AVIATION...Wimberley