743
FXUS62 KGSP 251355
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
955 AM EDT Wed Jun 25 2025

.SYNOPSIS...
Heat and humidity remains elevated today, as a large upper level
high dominates over the region. The upper ridge will begin to
weaken, however, allowing for scattered to numerous showers
and thunderstorms this afternoon through this evening. The high
will continue to break down gradually over the next few days,
resulting in less oppressive heat, but still humid conditions. An
upper disturbance will linger over the Southeast states, resulting
in increased shower and thunderstorm chances across the area each
day through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 946 AM Wednesday...

Key Messages:

1) Hot and Humid Again Today with Triple Digit Heat Indices
Expected Again, Mainly East of the North Carolina Mountains

2) Heat Advisory Remains in Effect through 8 PM

3) Strong to Severe Storms this Afternoon and Evening with the Main
Hazard being Damaging Wind Gusts but brief large hail will also be
Possible

A hot and humid start to the day with many locations already seeing
temperatures in the upper 80s to low 90s at 10am. This would support
another day of widespread highs in the upper 90s to near 100, with
low 90s in the mountain valleys. Speaking of, valley fog is once
again slowly mixing out in the Little Tennessee Valley and should be
gone within the next hour or so. The severe weather forecast remains
on track as well with a rather volatile atmosphere for damaging
microbursts taking shape. Morning 12z RAOBs from Peachtree City, GA
and Greensboro, NC already depict a moderately unstable environment.
Modified soundings based on expected afternoon temperature and
dewpoint paints 4500-5000 J/kg of surface-based CAPE across the
region along with 1200-1400 J/kg of downdraft CAPE. Lapse rates will
also be very steep for the summer with large surface delta ThetaE
values. Parameters from the modified soundings were run through the
local microburst checklist with microburst composite values of 13 at
Greensboro and 10 at Peachtree City, both of which are indicative of
an extremely favorable environment for damaging winds. Morning
mesoanalysis depicts a weak surface boundary near the Virginia/North
Carolina border that will drop south along the I-85 corridor. This,
in conjunction with a subtle inverted trough along the east coast,
will be the impetus for numerous thunderstorms this afternoon.
Additional storms will likely initiate over the mountains,
especially along the I-26 corridor. Eventually, activity will grow
loosely upscale along composite cold pools.

Otherwise, the large, hot upper anticyclone that has been situated
over the eastern United States the last few days will gradually
break down through the period while a weak upper low tracks over
Florida. Despite the upper ridge weakening, we can expect another
hot and humid day. The weakening ridge will also allow shower and
thunderstorm chances to return area-wide this afternoon and evening.

Highs will rebound back into the mid to upper 90s east of the
mountains and the upper 80s to lower 90s in the mountain valleys. A
few isolated locations may even reach 100 degrees F. With dewpoints
not expected to mix out much today (ranging from the upper 60s to
mid 70s) heat indices will once again reach the triple digits mainly
east of the North Carolina mountains. However, the Caldwell, Burke,
McDowell, Rutherford, and Polk mountain zones will see triple digit
heat indices again. So, the Heat Advisory for the SC Upstate, the NC
Foothills and Piedmont, portions of NE GA, and the Caldwell, Burke,
McDowell, Rutherford, and Polk mountain zones remains in effect
through 8pm this evening as heat indices will range from 105 to 109
degrees F during peak heating. The wrinkle in the forecast regarding
high temps and heat indices is that scattered to possibly numerous
thunderstorms may develop this afternoon and evening which may limit
temps and heat indices somewhat. However, with activity not really
expected to blossom until ~3-6 pm we may still be able to see most
locations in the Heat Advisory reach criteria this afternoon.

Speaking of the thunderstorm potential this afternoon and evening,
confidence on the overall coverage and exact timing of activity is
low as the 06Z CAMs are not in great agreement. The HRRR is the most
bullish with activity and depicts numerous thunderstorms this
afternoon into the late tonight across much of the forecast area.
The latest hourly runs of the HRRR also seem to be trending an hour
or two later than the 06Z, with activity not developing until ~5-7
pm. The rest of the CAMs show more scattered activity and a slightly
earlier start time ~1-3 pm and have activity waning from roughly 8pm
to 11pm. However, the NAMNest does show the potential for convection
to linger through late tonight as well. Regardless of when activity
finally develops this afternoon, strong to severe storms can be
expected with both SBCAPE and MLCAPE values ranging from 2,500-
3,500+ J/kg during peak heating. With model soundings having an
inverted-V profile and depicting 1,000-1,500+ of DCAPE available
this afternoon, damaging wind gusts from microbursts can be expected
with any severe storms that develop. Brief, large hail will also be
possible. The SPC Day 1 Severe Weather Outlook has the entire
forecast area in a Slight Risk for severe storms and this appears
warranted based on how unstable the environment will be today. The
entire forecast area is also in a Marginal risk for excessive
rainfall and this also appears warranted as deep layer shear will be
very weak (10 kts or less) allowing for fairly slow storm movement.
Slow storm movement combined with locally heavy rainfall may lead to
isolated instances of isolated flooding mainly in low-lying and poor
drainage areas.

Lows tonight will be a few degrees cooler east of the mountains
compared to this morning but will still end up ~6-9 degrees above
normal. Patchy fog and low stratus may develop overnight, especially
for areas that receive heavy rainfall this afternoon/evening.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
As of 230 AM EDT Wednesday: The upper ridge will continue to weaken
thru the rest of the workweek, as a weak subtropical low drifts
toward the NW over FL and settles over the Southeast. The low opens
up and merges with a northern stream trough to keep a weakness
in the subtropical high over the region into the weekend. Temps
will remain slightly above normal (mainly lower to mid 90s in
the Piedmont), which with dewpts in the upper 60s to lower 70s
should keep heat indices in the 98 to 104F range. If we end up
with less convection today than expected to overturn the air mass,
there is a possibility that Thursday`s highs may be slight higher
and heat indices may reach 105 or higher, necessitating a Heat
Advisory. Friday`s conditions look similar to Thursday. PoPs both
days feature solid likely to categorical in the mountains, tapering
to 30-40 percent range southeast of I-85. We shouldn`t be as
unstable as today, but a few severe pulse storms will be possible.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 245 AM EDT Wednesday: Little change in the pattern over the
weekend, as a weakness in the subtropical ridge remains over the
Southeast. Continued enhanced diurnal PoPs and slightly above normal
temps looks to continue thru at least Monday. The 00z guidance is in
good agreement on a deeper northern stream trough entering the Ohio
Valley Tuesday. This may bring a cold front close to the forecast
area and enhance convection even further. There may be an uptick in
severe tstm risk as well, as the entrance region of an upper jet
dips south. With plenty of cloud cover and decent precip coverage
each day, expect temps to trend down toward normal and heat indices
should remain below advisory criteria. A few severe microbursts
and isolated flash flooding will also be possible each day.

&&

.AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
At KCLT and elsewhere: Dry conditions will continue through at
least the late morning hours before TSRA chances return this
afternoon and evening. Maintained TEMPOs across all terminals from
20Z to 24Z (19Z-23Z for KAVL) for +TSRA and associated restrictions
as strong to severe thunderstorms are likely to develop. Microbursts
will be a concern with any severe thunderstorms that develop. Went
with PROB30s across the terminals for TSRA and associated
restrictions this evening into late tonight as activity may linger.
Confidence on the TEMPO timing remains low as guidance is not in
great agreement regarding when exactly storms will develop. Guidance
is also not in agreement regarding how late storms will linger so
confidence on PROB30s is also low. It will remain VFR through the
12Z TAF period outside of TSRA. FEW to SCT cumulus field will return
this afternoon and evening with SCT to BKN cirrus overhead. Winds
will be mostly calm to light and VRB through the TAF period. Patchy
fog and/or low stratus may develop again overnight across the
mountain valleys. Confidence on whether this will reach KAVL remains
low.

Outlook: Daily chances for afternoon and evening showers and
thunderstorms continue into the weekend. Fog and/or low stratus will
be possible each morning in the usual mountain valleys as well as
near lakes and rivers.

&&

.CLIMATE...
RECORDS FOR 06-25

               MAX TEMPERATURE         MIN TEMPERATURE
  STATION      HIGH        LOW         HIGH        LOW
  -------  ----------  ----------  ----------  ----------
   KAVL      96 1952     63 1889     69 1949     45 1972
                                        1943
                                        1891
   KCLT     102 1914     70 1980     75 1952     53 1889
                            1915        1914
                            1889
   KGSP     101 1952     69 1980     75 1931     52 1972
                                        1925


&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028-
     029.
NC...Heat Advisory until 8 PM EDT this evening for NCZ035>037-056-
     057-068>072-082-501>510.
SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019-
     101>109.

&&

$$

SYNOPSIS...ARK
NEAR TERM...AR/TW
SHORT TERM...ARK
LONG TERM...ARK
AVIATION...AR
CLIMATE...