180
FXUS62 KGSP 221810
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
210 PM EDT Sun Sep 22 2024

.SYNOPSIS...
High pressure will linger across the region the remainder of the
weekend, keeping hot temperatures across the board. A more moist
airmass will spread over the area on Monday and linger through at
least mid-week.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 205 PM EDT: An upper ridge axis to our west will become
centered over the Appalachians by the end of the period. However,
short wave energy is able to top the ridge and move into the area. A
dampening short wave overnight and a stronger one Monday. CAMs
continue to highlight the area along and west of the I-26 corridor
for mainly isolated convection this afternoon and evening. The
northern mountains and I-40 corridor are highlighted for isolated
convection with the wave overnight. Expect low clouds to spread into
the area from the NE toward daybreak. This should limit patchy fog
except for the usual mountain valley fog. Lows Ohio Valley could
wander toward the southern Appalachians toward daybreak Monday. Lows
will be 5-10 degrees above normal.

Expect scattered mainly diurnal convection to develop along and
north of the I-85 corridor with numerous coverage possible across
the mountains. While severe storm chances will be better of TN,
instability, shear, and DCAPE values will be high enough for a storm
or two to produce damaging wind gusts. Highs will be around 5
degrees above normal.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
As of 129 PM EDT Sunday: Potent subtropical ridging will be in place
over the Gulf of Mexico Monday evening, while a longwave trough will
deepen over the Great Plains as multiple embedded vort lobes phase
together as they move east.  This`ll have the effect of driving
ridging over the Carolinas eastward on Tuesday, and exposing us to
increasingly potent moisture ahead of the advancing trough.  Between
cloud cover and diminishing thicknesses, temperatures will fall on
Tuesday, with highs only climbing into the low- to mid-80s...and
scattered showers can be expected across the forecast area.  A
surprising 1200+ J/kg sbCAPE will develop east of the mountains,
permitting some embedded thunder as well.

Wednesday, an upper low will cutoff from the main trough and settle
over the Ozarks.  Meanwhile, a broad baroclinic zone will settle
into the central Ohio Valley, apparently stalling somewhere west of
the NC-TN border. Based on the latest 12z suite of operational
guidance, it should remain far enough displaced from our region that
it won`t contribute to significantly high rain chances on Wednesday
compared to Tuesday...but we`ll still be locked into a moist air
mass, with another round of respectable afternoon instability...so
at least widely scattered showers and thunder appear likely.  Highs
on Wednesday will be similar to Tuesday`s with most locations
cooling only a degree or two.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
As of 140 PM EDT Sunday: By Wednesday evening, the bulk of guidance
is in agreement on a developing tropical low over the Gulf of
Mexico, somewhere west of Cuba.  On Thursday and Friday, this system
is expected to lift north.  The exact configuration of the upper
pattern when the system begins to move inland will have a large
impact on what impacts are realized here in the Carolinas.  Ensemble
members with a weaker Ozark low and stronger ridge over the Eastern
Seaboard depict the post-tropical system tracking well west of the
Carolinas, while members with stronger Ozark lows and weaker east
coast ridging depict a more eastward track, which would bring more
moisture into the Carolinas.  The second solution is the dominant
one among the latest LREF cycle, but not by much - there`s still
significant support for a more westward track.

Having said all this...either solution would bring some moisture
into the Carolinas by Friday and Saturday...it`s just a question of
how much.  With that in mind...spectulating on possible rainfall
totals is still a losing game.  It`s likely to be rainy Friday and
Saturday, but QPF remains low-confidence.  Otherwise...the remainder
of the forecast is murky, with the evolution of the atmosphere past
Friday and Saturday completely dependent on how the tropical system
affects our area.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
At KCLT and elsewhere: VFR cumulus this afternoon with isolated
convection generally along and west of I-26. Chance still too low
for TAF mention. MVFR then IFR stratocu moves SW across the area
late this evening and overnight. Have it for the NC sites, where fog
may also develop at KAVL and KHKY. There is a chance the cloud deck
makes it to KGSP/KGMU, but that is more uncertain so put FEW MVFR
for now. Vsby should improve quickly after daybreak, but cigs will
take longer to go VFR. Scattered convection expected during the
afternoon, so have PROB30 at KAVL where it starts sooner and KCLT
wit the longer TAF period. Light N to NE wind becomes through the
overnight becomes light S on Monday.

Outlook: A weak cold front will slowly approach from the west this
week before tracking over the area on Thursday. Chances for diurnal
showers and thunderstorms will increase Monday and remain elevated
through at least Thursday. A tropical cyclone may move into the SE
late in the week. Mountain valley fog/low stratus may develop each
morning around daybreak.

&&

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

&&

$$

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