748
FXUS62 KGSP 281107
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
707 AM EDT Tue Jul 28 2026

.WHAT HAS CHANGED...
Updated aviation section for 12z TAFs.

Made tweaks to PoPs/sky cover this morning in order to better
reflect activity approaching from the north.

&&

.KEY MESSAGES...
1. Any thunderstorms developing ahead of a cold front today and
this evening will pose a risk of severe weather. Confidence has
increased on occurrence and timing though still a bit lower than
we would typically have at this point. The main hazards with any
severe storms are damaging winds and large hail. Make sure you
have multiple ways to receive warnings.
2. Hot and humid today. A Heat Advisory remains in effect
for northeast Georgia from noon to 8 PM. Stay hydrated, limit
time outdoors and spend as much time in air conditioning as
possible. Never leave people or pets alone in a closed car. Look
before you lock!
3. Less humid, drier, and cooler behind the front Wednesday
through Friday. Even cooler conditions expected over the weekend
with shower and thunderstorm chances returning.

&&

.DISCUSSION...
Key message 1: Any thunderstorms developing ahead of a cold
front today and this evening will pose a risk of severe
weather. Confidence has increased on occurrence and timing though
still a bit lower than we would typically have at this point. The
main hazards with any severe storms are damaging winds and large
hail. Make sure you have multiple ways to receive warnings.

We`ll have more day in the active, northwest-flow "ring of fire"
pattern we have been locked into since late last week.  A well
defined shortwave and surface low now between Lakes Michigan and
Erie is associated with a cold front which is tracking thru the OH
Valley. A loosely organized cluster of storms now in West Virginia
will approach the area this morning but looks more likely to track
toward central NC, just clipping the NE corner of our CWA. New
development farther west in KY is along the same axis ahead of
the front, and if that grows upscale it would be more likely to
move into the NW CWA by late morning--a scenario which appeared
plausible based on the analysis made overnight. CAMs have continued
to trend away from the idea of these storms growing into a line
as some earlier runs suggested. Made adjustments to PoPs with the
daybreak update in order to better handle the expected track;
this reduced PoPs in the western SC and GA zones in the first
half of the day but maintains chance to likely values over the
NC mtns. Anomalously strong flow in the 700-500mb layer leads
to effective shear perhaps exceeding 40 kt along/west of the
Appalachians this morning, and 2000 J/kg or more of MUCAPE may
be present. Thus there would appear to be some risk of organized
severe weather with this morning activity, though the northerly
shear vectors do suggest updrafts may remain discrete and could
develop into supercells.

Cloud cover associated with the prefrontal WAA, and/or cirrus
debris from the morning storms, still could inhibit convective
development later in the day, though without a strong cold pool
from an MCS it`s hard to see that completely capping off profiles
and thus is unlikely to preclude a second round of activity
nearer the actual cold front, this afternoon and evening. PoPs
are lower in the afternoon for the southwest quadrant of the CWA,
where the morning activity (and arguably strong downslope flow)
has the most potential to keep things quiet. PoPs are highest in
the afternoon along the TN border for upslope, but also in the
eastern Piedmont south of I-85, where morning activity is likely to
have the least effect. However we will have to monitor convective
trends and surface obs throughout the morning to evaluate the
likelihood of the second round taking shape. By late afternoon or
early evening, assuming no inhibition, 2000-3000 J/kg of SBCAPE
still may overlap with 40+ kt of northwesterly 0-6km bulk shear
(and strongly curving hodographs). As the cold front looks to
advance SE`wd through the NC Piedmont accompanied by the shortwave,
discrete supercells remain the favored mode there. Damaging winds
and large hail perhaps approaching 2" in diameter are certainly
on the table this afternoon, but 0-1km helicity exceeds 100 m2/s2
in some areas and a tornado cannot be ruled out. Farther west,
the frontal orientation is more E-W and a more linear mode may
result, though still with wind/hail risk from embedded supercell
structures. SPC Day 1 outlook remains Slight Risk for virtually
the whole CWA, but with the probabilistic contours more suggestive
of the greatest threat being in our eastern zones.


Key message 2: Hot and humid today. A Heat Advisory remains in effect
for northeast Georgia from noon to 8 PM. Stay hydrated, limit time
outdoors and spend as much time in air conditioning as possible.
Never leave people or pets alone in a closed car. Look before
you lock!

Still expecting today to be the hottest and most humid day this
week. Heat index will flirt with 105 in a few scattered locations
in the lower Piedmont; the contiguous area of 105+ heat indices
in a portion of NE GA warranted issuance of a Heat Advisory
there. Considered expansion into some counties in the SC Lakelands,
but there is too much uncertainty about how morning convection
may affect temperatures there and elsewhere in the Piedmont for
that matter.


Key message 3: Less humid, drier, and cooler behind the front
Wednesday through Friday. Even cooler conditions expected over
the weekend with shower and thunderstorm chances returning.

Behind the front, temperatures trend back to around climo on
Wednesday, with lower humidity that should keep indices below 100,
and much more stable conditions such that precip chances remain near
zero, except for the TN/NC border area where upsloping could kick
off a shower or two. Appreciably drier air filters in for Thursday
that brings temps slightly lower but heat indices more noticeably
lower. Similar conditions last through Friday. The Upstate and NE
GA, being warmer, actually see RH fall to around 35% Thursday and
Friday, which is exceptionally low for this time of year. A few
spots with enhanced mixing could go even lower.

The Western ridge / Eastern trough pattern lingers into next
weekend, though not as unstable upstream and MCS threats do
not look to recur.  Precip/storms may return Saturday, when a
reinforcing shortwave or upper low rotates into the Eastern trough
and reactivates a warm front over the Southeast; PoPs are now likely
for Sunday. The 00z GFS and ECMWF actually seem to occlude the low
to our west by Sunday, whereas the Canadian GDPS maintains an open
wave, which is more similar to earlier solutions. Thus confidence
and PoPs decrease Monday given the spread in the speed of the low
pressure system. Temperatures do remain mild, likely at least a
little below normal.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
At KCLT and elsewhere: Winds will be light/VRB at the beginning of
the period but will pick up from the SW 13-16z with diurnal mixing
(exc. NW at KAVL) and gusts of 20 kt are expected to be common
around the area by midday. Conditions are favorable for storms
to form to our north and west during the morning, ahead of an
approaching cold front. A weakening band of SHRA perhaps with an
embedded TS may reach the sites between 15-18z; included VCSH and
an uptick in high altitude cloud cover around that time everywhere
except KAND. With that activity looking unlikely to bring a cold
pool to the area, confidence has increased for TSRA impacts later in
the afternoon to early evening. Went with PROB30s at KAVL and the SC
sites in part due to less confidence on timing, though confidence
has increased on occurrence; if timing confidence increases these
PROB30s could easily be replaced with TEMPOs. At KCLT and KHKY the
timing confidence is better and promotion to TEMPO has already been
done. Environmental factors suggest TSRA will easily produce strong
outflow winds and torrential downpours, pose a threat of localized
damaging winds, and with greater than normal hail potential than
most storms in this area this time of year. VRB gusts to 30 kt and
IFR vsby in the conditional groups. Activity should shift out of
the region this evening as the front passes, and winds shift to
NW at all sites behind the front. A few SHRA could develop near
KAVL overnight due to upslope flow into the mtns. Post-frontal
drying could inhibit fog formation tonight but can`t rule out some
shallow fog after 06z especially where heavy rain falls today.

Outlook: Dry and mostly VFR conditions return Wed thru Fri, with
shower and thunderstorm chances and their associated restrictions
returning over the weekend. Low stratus and/or fog will be possible
each morning, mainly in the mtn valleys.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from noon today to 8 PM EDT this evening for
     GAZ018-026-028-029.
NC...None.
SC...None.

&&

$$

JCW