-- Discussion containing changed information from previous version are highlighted. --
752
FXUS62 KGSP 231039
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
639 AM EDT Mon Sep 23 2024

.SYNOPSIS...
A moist airmass will spread over the area today and linger
through mid-week. A tropical system is expected to strengthen
over the Gulf of Mexico on Thursday and will likely impact our
area by the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 630 am: A narrow inverted surface ridge/associated E/NE flow
is nosing into the area this morning, and a wedge of low stratus
east of the Blue Ridge escarpment has pushed SW almost to the
Georgia border. This cloud cover may push as far southwest as
extreme northeast GA by around sunrise before stalling. As an upper
ridge axis shifts east of the forecast area later this morning, so
will the surface ridge shift to near the East Coast, and clouds are
expected to steadily scatter from the SW throughout the late morning
into the afternoon. This will allow for good heating and
destabilization, with afternoon sbCAPE expected to range from
1500-2000 J/kg across the western half of the area. The temp
forecast will be a bit tricky today due to the varying cloud cover,
but max temps are forecast to range from around 10 degrees above
climo again across the western third of the area, to close to normal
in the cloudier locations across the northeast corner of the CWA.

With the synoptic pattern becoming broadly more favorable for
convective development, especially as a short wave trough approaches
from the TN Valley this evening, scattered diurnal convection is
expected to develop across the high terrain during mid-late
afternoon, with coverage enhancing and moving off the escarpment
into the foothills and Piedmont this evening as the short wave
approaches. Mountain PoPs generally peak in the 50-60% range this
afternoon, while the highest Piedmont chances (40-50%) are withheld
until after 00Z. A combination of moderate instability and improving
deep layer shear (~35 kts by the end of the day) may be just enough
to support a brief severe storm or two. Convective coverage and
intensity will steadily wane beginning around late evening, but
slight chance PoPs linger for at least part of the area through 12Z
Tuesday. Min temps will again by 5-10 degrees above normal.
-- End Changed Discussion --

&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 3:15 AM EDT Monday: The short-term fcst picks up at 12z on
Tuesday with upper ridging still in place over the Southeast. Over
the next 24 hrs or so, the upper pattern amplifies as broad upper
trofing digs down over the central CONUS. By the end of the period
early Thursday, a fairly large upper low is expected to spin off
from the main trof as the trof itself lifts back northward. This
upper low is progged to be centered to our west and over Arkansas
by the end of the period. At the sfc, another low will spin up over
the Ohio River Valley on Tuesday and bring another weak cold front
to our doorstep by early Wednesday. This front is now expected to
stall out just to our west late Wednesday into Thursday with the
broad area of high pressure behind it remaining to our NW. At the
same time, a tropical low will strengthen over the Gulf of Mexico
and track northward as the period is ending early Thursday. As for
the sensible fcst, no major changes were needed for Tuesday or Wed-
nesday with likely PoPs carried over the northern half of our CWA
for both days. Temperatures will cool somewhat thru the period, yet
highs will still likely top-out just above climatology on Wednesday,
especially over our southern zones.

&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 3 AM EDT Monday: The extended forecast picks up at 12z
on Thursday with upper ridging still in place just to our east
and a fairly large upper low centered to our west over Arkansas.
At the same time, the upper low associated with a tropical sys-
tem in the Gulf of Mexico will lift northward on Thursday and
then rotate around the other low in response to the Fujiwhara
effect late Thursday into Friday. Another upper low is still
expected to develop over New England on Friday, but most of
the long-range guidance now has it moving offshore as we go
into the weekend. Over the weekend, the tropical low is expec-
ted to get absorbed by the larger upper low over Arkansas. By
the end of the period early next week, the upper low is expec-
ted to gradually drift north and open back up to the northern
stream flow. At the sfc, a weak but moist cold front will stall
out over our area just before the period begins, while broad
high pressure remains well to our NW. At the same time,  a
robust tropical low will strengthen over the Gulf of Mexico
and track north. Most of the current model guidance has it
moving onshore over the Florida Panhandle late Thurs and then
over our area early Fri. Based on the current guidance, the
center of the low is likely to pass over the western extent
of our fcst area (or just west of it) on Fri and then quickly
lift NW of our area and dissipate as we go into the weekend.
At this time, it`s looking like the main impacts to our fcst
area from this tropical system will be heavy rainfall and some
gusty winds on Thursday and Friday. Confidence should increase
wrt to these impacts over the next few days.

&&

.AVIATION /12Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
At KCLT and elsewhere: IFR cigs have overspread much of the Terminal
Forecast Area this morning, with LIFR conditions being reported at
KHKY and low MVFR at KAVL. Expect at least tempo LIFR for at least a
couple of hours this morning...except at KAND and KAVL, where the
flt category should remain at or above IFR. Cigs should improve to
VFR by late morning at KAND/KAVL...but IFR/low MVFR conditions
should linger into the afternoon at the other sites, with VFR likely
not developing until mid/late afternoon. As clouds begin to thin
from the SW throughout the morning and afternoon, instability is
expected to develop, fueling the potential for scattered diurnal
convection. Scattered convection should initially develop over the
high terrain, then 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. Restrictions in low cigs are
expected to return to the area tonight, with at least IFR...if not
LIFR likely developing prior to daybreak Tue. There is also higher
potential for visby restrictions...and 2-4SM is advertised at most
sites to coincide with the lowering cigs.

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. Fog/low stratus may develop each morning,
especially in the mountain valleys. 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...JPT
NEAR TERM...JDL
SHORT TERM...JPT
LONG TERM...JPT
AVIATION...JDL