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891
FXUS62 KGSP 230601
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
201 AM EDT Mon Sep 23 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 TODAY/...
-- Changed Discussion --
As of 155 am: An upper ridge axis to our west will become centered
over the Appalachians by the end of the period. However, a dampening
short wave will track overhead overnight with a stronger shortwave
expected later today into this evening. May see a stray shower or
two later this morning over the northern mountains and I-40
corridor, but confidence is low. Low clouds are already quickly
filling in across the NC Piedmont, and will spread steadily SW
through the morning...likely reaching U.S. Highway 25 or so by
sunrise before slowing. This should limit patchy fog except for the
usual mountain valley locations. 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 by late this afternoon. While severe storm chances
will be better to our west, instability, shear, and DCAPE values
will be high enough for a storm or two to produce damaging wind
gusts in our area. Highs will be around 5 degrees above normal.
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&&

.SHORT TERM /TONIGHT 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 /06Z MONDAY THROUGH FRIDAY/...
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At KCLT and elsewhere: Low clouds are already filling in across
western NC, particularly at KHKY and KCLT, which are already
reporting low MVFR cigs. These low clouds will spread steadily SW
through the morning, reaching KAVL/KGSP/KGMU by daybreak. Cigs will
eventually lower to IFR, likely bottoming out at LIFR around sunrise
before improvement begins during late morning. Some MVFR
restrictions are also possible, but low cigs will be by far the
bigger concern. As skies begin to clear from the SW throughout the
morning and afternoon, instability is expected to develop, fueling
the potential for scattered diurnal convection. Convection should
initially develop over the high terrain, but will likely spread
across the remainder of the Terminal Forecast Area during the
evening, as an upper level disturbance approaches. Prob30s for TSRA
are featured at all sites, favoring the afternoon and early evening
at KAVL, and primarily the evening hours at the other sites. Winds
will remain light through the period, with directions generally
being E/NE this morning, turning toward the E/SE during the daylight
hours.

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. Confidence is increasing that
a tropical cyclone, with attendant heavy rain and possible strong
winds will pass over or near the area late in the week.
-- End Changed Discussion --

&&

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

&&

$$

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