Severe Thunderstorm Warning 63, NWS Greenville-Spartanburg, SC

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
229 PM EDT Sat Jun 27 2026

.WHAT HAS CHANGED...
Updated the aviation discussion for the 18Z TAFs. Otherwise, little
change of significance has been made to the forecast.

&&

.KEY MESSAGES...
1. Shower and thunderstorm chances linger through the
weekend. Isolated severe storms capable of producing damaging
wind gusts are possible, mainly during the afternoon/evening.
2. Heat risk will steadily increase through next week, with heat
indices potentially exceeding 100 degrees across much of the
Piedmont and foothills...especially from mid-week on.

&&

.DISCUSSION...
Key message 1: Shower and thunderstorm chances linger through the
weekend. Isolated severe storms capable of producing damaging wind
gusts are possible, mainly during the afternoon/evening.

Convection continues to steadily expand in coverage and
intensity this afternoon within a moderately unstable
environment characterized by sbCAPE of 2000-2500 J/kg. By late
afternoon...scattered-to-numerous coverage is expected across much
of western NC...where westerly flow will result in a combination of
upstream convective clusters moving into the CWA and MCVs embedded
in the mid-level flow initiating new convection. While deep layer
shear is seasonably modest, 0-3 km shear of 15-25 kts should be
sufficient to allow for small clusters of convection to organized
along outflows...posing a threat of locally strong-to-briefly
damaging wind gusts, with pulse updrafts and cell mergers posing
an additional risk of brief microbursts.

Diurnal convection should generally wind down this evening. However,
convection is forecast to blossom and become at least somewhat
organized this afternoon/evening within a very unstable air
mass across the mid-Miss Valley on the east side of building
upper ridge. There's a decent signal in convection-allowing
models and associated ensemble guidance that remnants of this
activity will move into the southern Appalachians at some point
during the 09-15Z Sunday time frame. Considering the time of
day/limited instability and lack of stronger shear to maintain
a high degree of organization, the potential for severe weather
will be low in our area during this time, but can't rule out
some isolated strong-to-damaging wind gusts as this activity
makes its initial push into the area tomorrow morning. The
possibility...if not likelihood of morning convection creates a
considerable amount of uncertainty regarding diurnal convective
trends Sunday afternoon/evening. Remnant outflow could create
renewed potential for stronger convective development across the
Piedmont if timing of convection is late enough to interact with
destabilization...or if convection is early enough in the day
to allow for good recovery. Sunday PoPs peak at likely over the
mountains Sunday morning, with generally token chance PoPs carried
in all areas during the afternoon.

Temperatures will be a little above normal through Sunday
night. Heat Index is forecast to at least approach the century
mark across the southern ties of forecast zones Sunday afternoon,
but it is unlikely that occurrence of H.I. criteria of 105 will
be reached on anything more than a localized basis.

Key message 2: Heat risk will steadily increase through next week,
with heat indices potentially exceeding 100 degrees across much
of the Piedmont and foothills...especially from mid-week on.

An anticyclone and associated ridge will build across the TN
and OH Valleys early in the new work week, with the center of
the anticyclone forecast to build into the southern/central
Appalachians by the end of the week. This will allow the heat to
steadily build across the Southeast, with temperatures of around
5 degrees above climo during the first half of the week forecast
to increase to almost 10 degrees above normal by the start of the
holiday weekend. Maximum daily Heat Index is expected to be around,
or a little over the century mark, but still below Heat Advisory
levels through Wednesday, with greater potential for criteria to
be met Thursday through Saturday. This is all quite uncertain at
this time...and serves as a reminder that H.I. is very sensitive
to dewpoints...which sometimes mix out more than anticipated during
subsident regimes.

Otherwise, the more suppressed synoptic pattern is expected to
result in limited coverage of diurnal convection...especially from
Tuesday onward, when isolated to perhaps widely scattered activity
is forecast to be largely confined to the mountains.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
At KCLT and elsewhere: Convection will continue to gradually
increase in coverage and intensity through late afternoon.
Convection is most likely at the western NC terminals, and TEMPOs
for TSRA are carried at those TAF sites at some point during the
afternoon/evening. Probabilities are lower at the upstate SC
terminals, and Prob30s are carried this afternoon/evening at KGMU/
KGSP. Gusty and erratic outflow winds and briefly reduced visby are
expected with any TSRA. The convective potential is lower at KAND,
but isolated SHRA were already developing in the general area as of
early afternoon, so opted to start them off with a VCSH.

Otherwise, SW winds of 8-12 kts are expected this afternoon
everywhere except KAVL (where lighter winds are expected).
Convection should diminish across much of the area by mid/late
evening. While VFR conditions are forecast for the overnight, can't
rule out some areas of fog and/or low stratus developing, especially
in locations that receive appreciable rainfall this afternoon/
evening. However, this is very uncertain at this point, so VFR is
generally forecast with the exception of some MVFR fog at KAVL. High
resolution guidance has consistently depicted a complex of decaying
convection moving into the area from the NW at some point Sunday
morning, so VCSH or Prob30s for -TSRA are carried at most sites at
some point between 12-18Z Sunday.

Outlook: Isolated-to-widely scattered diurnal convection is expected
Sunday afternoon and again Monday. After Monday, diurnal showers and
storms are expected to become more confined to the mountains.
Mountain valley fog/low stratus will possible each morning.

&&

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

&&

JDL

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