551
FXUS62 KGSP 222321
AFDGSP

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

.SYNOPSIS...
High pressure lingers through tonight keeping well above normal
temperatures around. A moist airmass returns on Monday and lingers
through at least mid-week. Increased cloud cover and precipitation
will allow for a gradual cooling trend through the workweek.

&&

.NEAR TERM /THROUGH MONDAY/...
As of 550 PM EDT Sunday: No major changes were needed as the
forecast remains on track this evening. A few spotty showers are
noted west of I-85 in the NW SC Upstate, with some isolated showers
also tracking across the SW NC mountains this evening. Maintained
slight chance PoPs across these areas through the next few hours to
account for this activity.

Otherwise, an upper ridge axis to our west will become centered over
the Appalachians by the end of the period. However, a short wave is
able to round the ridge and move into the area this evening. A
dampening short wave will track overhead overnight, with a stronger
shortwave expected on 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...speculating 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 /00Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: KAND is expected to remain dry and VFR
through the 00Z TAF forecast period. The rest of the terminals will
see VFR conditions linger through late tonight before cigs gradually
lower overnight into daybreak Monday from northeast to southwest.
Patchy fog may develop as well so have TEMPOs (everywhere except
KAND) for MVFR fog and IFR cigs starting at 10Z-11Z and lasting
through 14Z-15Z. Cigs will be slow to recover, especially at KCLT
and KHKY. Thus, cigs may not lift to MVFR/VFR levels until late
Monday morning or early Monday afternoon. Isolated showers are
floating around the western half of the forecast area as of 00Z but
these are not expected to impact any of the terminals. Thus, dry
conditions should linger through Monday morning. Better coverage of
showers and thunderstorms can be expected Monday afternoon into
Monday evening so have PROB30s (everywhere but KAND) to account for
this activity. Winds east of the mountains will generally have some
E`ly component through the period, toggling from NE to E to SE at
times. Winds at KAVL will generally be light and VRB through Monday
morning before turning S`ly Monday afternoon.

Outlook: A weak cold front will slowly approach from the west this
week before tracking over the area on Thursday. This will allow the
chance for diurnal showers and thunderstorms to remain elevated
through at least Thursday. Mountain valley fog/low stratus may
develop each morning around daybreak. Tropical moisture may impact
the terminals late Thursday into late Friday.

&&

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

&&

$$

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