116
FXUS62 KGSP 231042
AFDGSP
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
642 AM EDT Mon Jun 23 2025
.SYNOPSIS...
The heat and humidity gradually increase through mid-week as a hot
upper ridge builds over the eastern United States. Isolated showers
and thunderstorms remain possible each afternoon and evening through
Tuesday, mainly across the mountains. The heat and humidity stick
around the rest of the week with daily shower and thunderstorm
chances area-wide Wednesday into the weekend.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 630 AM Monday: Forecast is on track, so no changes needed
with this update. Mountain valley fog has formed about where it
was expected and should dissipate quickly after sunrise.
Otherwise...heat will continue to build today, as the center of
a large warm upper level anticyclone remains over the Central
Appalachians. Subsidence from this system will continue to amplify
the heat, with temps expected to top out in the mid to upper 90s
across the foothills and Piedmont and into the lower 90s across
the larger mountain valleys. Dewpts should still mix out enough
to keep heat indices below 105, but cannot rule out a few spots
reaching a 105 heat index along the I-77 corridor. Have continued to
blend in the 10th percentile NBM, which has been verifying fairly
well the last couple days. So will hold off on a Heat Advisory for
today. With the high nearly right over the CWFA, guidance keeps even
most of the mountaintop convection suppressed this aftn. But it is
difficult not to see at least isolated showers and storms this time
of year, so will continue to show slight chc to low-end chc PoPs
along the ridgetops, especially near the TN border, where steering
flow will generally take the activity. Tonight will be muggy with
clear/mostly clear skies and light/calm wind. Some mountain valley
fog will likely develop. Lows will be a few degrees above normal,
in the 60s in the mountains and lower to mid 70s in the Piedmont.
&&
.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
As of 230 AM EDT Monday...
Key Messages:
1) Heat and Humidity Linger through the Period with the Most
Oppressive Conditions Expected on Tuesday
2) Heat Indices From the Upper 90s to Lower 100s Expected
Each Afternoon, Mainly East of the Mountains
3) It Will Remain Warm and Muggy Each Night so Anyone without Access
to Air Conditioning will see Limited Relief through the Period
4) Isolated Diurnal Convection Possible in the Mountains Tuesday
with Better Coverage of Convection Possible Wednesday Area-Wide
Main change during the short term is the latest global guidance are
now breaking down the large upper anticylcone over the eastern US
faster compared to the last several runs. The hot, upper ridge
continues to dominate on Tuesday before gradually weakening Tuesday
night into Wednesday. The ridge looks to then completely breaking
down Wednesday evening into Wednesday night. So it appears that
Tuesday will be the most oppressive day with temps and humidity
ticking down slightly on Wednesday as the ridge weakens.
Highs on Tuesday will soar into the mid to upper 90s east of the
mountains, with the upper 80s to lower 90s across the mountain
valleys. Heat indices Tuesday afternoon will range mostly from 103-
108 degrees F mainly east of the mountains. However, some locations
across the South Carolina Mountains and the the McDowell, Caldwell,
Burke, Polk, and Rutherford mountains are also likely to see heat
indices ranging from 103-108 degrees F. Since Heat Advisory Criteria
ranges from 105-109 degrees F, a Heat Advisory will likely be needed
for at least some of the locations mentioned above. Isolated (and
mainly diurnal) convection will develop again, mainly across the
mountains, on Tuesday with the upper ridge expected to suppress
convective activity somewhat. Lows east of the mountains will only
fall into the mid to upper 70s Tuesday night so warm and muggy
conditions can be expected.
With the upper ridge expected to weaken on Wednesday, the heat and
humidity will lower a bit compared to Tuesday. Highs east of the
mountains should only climb into the mid 90s, with highs rebounding
in the upper 80s to lower 90s across the mountain valleys. Heat
indices should end up a few degrees lower compared to Tuesday, with
Heat Advisory criteria limited to the Upper Savannah River Valley
and the I-77 corridor. So a Heat Advisory may be needed once again
for these locations. Another consequence of the ridge breaking down
faster is that shower and thunderstorm chances look to increase in
coverage area-wide Wednesday afternoon into Wednesday evening.
Capped PoPs to chance for now as guidance is not in great agreement
regarding the coverage of convection and as activity could still be
suppressed somewhat despite the ridge weakening. If convection
manages to develop over portions of the forecast area Wednesday
afternoon, it could help limit the heat index somewhat. Lows
Wednesday night will end up a few degrees cooler compared to
Tuesday, especially east of the mountains. Regardless, warm and
muggy conditions are expected to continue.
&&
.LONG TERM /THURSDAY THROUGH SUNDAY/...
As of 300 AM EDT Monday...
Key Messages:
1) Hot and Humid through the Period but Less Oppressive Compared to
the Short Term
2) Temperatures Remain a Few to Several Degrees Above Normal
3) Better Chances for Showers and Thunderstorms through the Period
Weak Upper ridging remains over the eastern US through the period.
Meanwhile, a weak upper low will track over Florida Thursday into
Thursday night before lifting northward towards the Deep South and
the Carolinas. This pattern will allow for better influx of moisture
through the long term, leading to better chances for convection each
day. Have the highest PoPs (roughly 60%) confined to the western
half of the forecast area with slightly lower PoPs across the
eastern half (~ 30% to 50%) for now. While it will still remain hot
and humid through the period, it will be less oppressive compared to
the short term. Highs east of the mountains each afternoon will
range from the upper 80s to lower 90s, with the mountain valleys
seeing highs each afternoon from the mid 80s to lower 90s. Heat
indices will remain a bit elevated on Thursday, ranging from the
upper 90s to lower 100s east of the mountains. Heat indices on
Friday appear to remain mostly below 100 degrees F east of the
mountains but will increase slightly over the weekend across the
Upper Savannah River Valley and along/near I-77. These locations
could see heat indices rebound back into the upper 90s to lower
100s. For now it appears that we will remain below Heat Advisory
Criteria (less than 105 degrees F) through the period.
&&
.AVIATION /12Z MONDAY THROUGH FRIDAY/...
At KCLT and elsewhere: VFR conditions with light winds to continue
thru the period as high pressure remains overhead. Some fog has
formed in the typical mountain valleys, but not at any of the TAF
sites. A pop-up shower or TSRA is possible across the mountains
this afternoon, but unlikely to affect KAVL. Expect aftn Cu to
develop across the area, then quickly dissipate after sunset.
Outlook: Dry conditions to continue thru Tuesday. Then a return
to more scattered to numerous diurnal showers and storms starting
Wednesday thru the end of the workweek. Fog and/or low stratus
will be possible each morning in the usual mtn valleys and near
lakes and rivers.
&&
.CLIMATE...
RECORDS FOR 06-23
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 93 2016 64 1936 70 2017 47 1947
1988
KCLT 100 2015 63 1936 77 2016 53 1947
KGSP 99 1988 70 1900 75 2016 54 1972
1944 1947
RECORDS FOR 06-24
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 94 1952 66 1991 70 2015 48 1947
1919 1918
KCLT 102 1930 68 1936 76 1998 55 1972
1914 1936
KGSP 100 1952 64 1936 76 2016 51 1915
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
RECORDS FOR 06-26
MAX TEMPERATURE MIN TEMPERATURE
STATION HIGH LOW HIGH LOW
------- ---------- ---------- ---------- ----------
KAVL 96 1948 65 1961 69 1952 49 1984
1974
KCLT 102 1952 68 1965 78 1948 55 1979
KGSP 100 1952 71 1991 77 1952 55 1979
1934 1974
1914
&&
.GSP WATCHES/WARNINGS/ADVISORIES...
GA...None.
NC...None.
SC...None.
&&
$$
SYNOPSIS...AR
NEAR TERM...ARK
SHORT TERM...AR
LONG TERM...AR
AVIATION...ARK
CLIMATE...