584
FXUS62 KCHS 220004
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
804 PM EDT Mon Jul 21 2025

.SYNOPSIS...
High pressure will prevail in the Atlantic through tonight,
with surface troughing inland. A weak front should stall over
or near our area Tuesday through Thursday, then dissipate on
Friday. Surface troughing returns this weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
The mid-level ridge has continued to become more and more diffuse as
vorticity on the western and eastern flanks causes the ridging
to lose cohesion. On the eastern flank, a TUTT remains quasi-
stationary southwest of Bermuda with pockets of PVA rippling
southeast from the Great Lakes on the backside of a long wave
trough axis. This has already allowed convective initiation to
occur across the upstate of GA, with a lee side trough centered
just northwest of the CWA. Along the lee side trough, convective
initiation is also occurring just southeast of Columbia, SC.

MLCAPE values are currently around 1500 J/kg with DCAPE values
nearing 900 J/kg. Steering flow is also forecast to collapse near a
pinned sea breeze this afternoon as the cloud layer steering flow is
forecast to be from the northwest at around 10 kt (advection
component) with the low level jet also being from the northwest at
around 10 kt (propagation component). This causes the net storm
motion to be near stationary. Storm could locally produce 2 to 4" of
rainfall. The other concern is the dry air located in the mid-levels
of the atmosphere. The dry air isn`t robust enough to inhibit CI,
but sufficient to increase DCAPE and the threat for localized
damaging wind gusts. As such, SPC has the area in a marginal risk.
WPC also has the area in a marginal risk for severe weather.

Finally, temperatures have reached the mid to upper 90s across the
region with heat index values generally in the 106 to 112F range. As
such, the heat advisory will remain in effect until 8 PM.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
The mid-levels will consist of a 594 dam ridge centered over the MS
Valley Tuesday morning. The ridge is expected to remain in place
through Thursday, expanding and strengthening slightly to about 595
dam over the Southeast U.S. At the surface, models have a weak cold
front moving south through our area Tuesday morning and afternoon,
then transitioning to a stationary front either over or just
offshore Tuesday night through Thursday. The location of the front
will keep ushering plenty of deep moisture into our area, with PWATs
exceeding 2", as well as provide a focus for at least scattered
convection each afternoon and evening.

As for the convective potential each day, Tuesday`s afternoon
thunderstorms have the potential to be strong to severe, with
damaging wind gusts being the main hazard. Forecast soundings
indicate there will be plenty of instability, with MLCAPEs peaking
around 1,500-2,000 J/kg and DCAPE values ~1,000 J/kg. While we
cannot rule out a strong to marginally severe storm Wednesday or
Thursday, the highest instability could remain south of our area.

Heavy rainfall is also a concern on Tuesday given PWATs upwards of
2.1", storm motions around 10 kt, and potential for training and/or
backbuilding. HREF guidance shows an average of a 40-70% chance for
rainfall totals of 2 inches or greater, mainly for areas away from
the immediate coast. Flood Advisories could be needed Tuesday and
the potential for a Flood Watch is also being considered.

As for temperatures, Tuesday will be the hottest day of the trio
with high temperatures ranging from the low to mid 90s across our
South Carolina counties and mid to upper 90s across our Georgia
counties. A Heat Advisory has been issued for most of the southeast
Georgia counties, along with Jasper and Beaufort counties in South
Carolina. In those locations, heat indices will peak in the 108-111
degree range. Elsewhere, heat indices should briefly peak around 103-
107 degrees, along with the expectation that the onset of convection
could be earlier for those areas. Therefore, we opted not to issue
Heat Advisories for the northern tier. Wednesday and Thursday,
temperatures look to be at or below normal, in the upper 80s to low
90s. Low temperatures will remain mild both Tuesday and Wednesday
night, falling into the low to mid 70s inland, and upper 70s/near 80
degrees along the beaches.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Mid and upper level ridging will become established just east of SC
with a mid-level weakness approaching the Appalachians by the end of
the long term. As this occurs, another lee side trough could develop
and help focus convection initially inland with outflows heading
towards coastal GA/SC. The exact details are still yet to be
determined, but either way will continue to carry at least a chance
of showers and thunderstorms each day. Temperatures will increase
over the weekend as the ridge centers over the forecast area, this
could lead to the potential for additional Heat Advisories.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
00Z TAFs: Showers and thunderstorms developed across Charleston
county this afternoon and also interior Georgia. The resultant
outflow from Charleston county is now southwest of KCHS/ KJZI,
and therefore no more precipitation is expected through tonight
for the Charleston terminals. Towards KSAV however, multiple
outflows are about to collide (from the west, south, and
southeast) with thunderstorms expected. Convection will then
come to an end at KSAV this evening. The primary threat with
these storms will be gusty winds and restrictions in
visibilities.

Tuesday: Initially dry weather and VFR conditions are forecast
ahead of an approaching cold front. In the afternoon,
widespread showers and thunderstorms are forecast to develop
along and ahead of a cold front. Restrictions in ceilings and
visibilities are likely with wind gusts during the
thunderstorms.

Extended Aviation Outlook: Expect brief flight restrictions
each afternoon/evening due to showers/thunderstorms.

&&

.MARINE...
Today and tonight: The sfc pattern will feature a trough over the
Midlands this morning, drifting over the Coastal Plain this
afternoon. HRRR shows the sea breeze remaining pinned to the coast
through late this afternoon. This pattern should yield southwest
winds around 10 kts through the near term. Wave heights are forecast
to range between 2 to 3 ft.

Tuesday through Saturday: A weak cold front will stall over or near
our coastal waters Tuesday through Thursday, then dissipate on
Friday. The front will cause surface winds to prevail from the NE or
E around 10-15 kts through Wednesday, before starting to veer on
Thursday. By Friday, a more typical summertime wind pattern will be
in place with High pressure in the Atlantic and troughing inland.
During the day on Friday, expect backing winds with the formation of
the afternoon sea breeze. The highest gusts will be along the
land/sea interface and across Charleston Harbor (with its passage).
Friday night, expect veering of the winds as a nocturnal jet tries
to set up close to shore. No marine concerns are expected through
the period.

Rip Currents: Increasing astronomical influences along with a modest
onshore flow will lead to a moderate risk for currents along all
area beaches Wednesday.

&&

.TIDES/COASTAL FLOODING...
Astronomical tides will rise with the upcoming new moon on Thursday.
Additionally, surface winds will turn from the northeast Monday
night and persist through midweek. This will cause tidal anamolies
to increase. Minor coastal flooding is possible with the Tuesday and
Wednesday evening high tides along coastal Charleston and coastal
Colleton Counties. Elevated tides could persist into Thursday.

&&

.CLIMATE...
Record High Minimum Temperatures:

July 21:
KCHS: 80/1986
KCXM: 83/1998
KSAV: 81/1942

July 26:
KCHS: 78/2012
KCXM: 82/2023

July 27:
KCHS: 80/2014
KSAV: 80/1885

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory from 11 AM to 8 PM EDT Tuesday for GAZ099>101-
     114>119-137>141.
SC...Heat Advisory from 11 AM to 8 PM EDT Tuesday for SCZ047-048-
     051.
MARINE...None.

&&

$$

NEAR TERM...Haines
SHORT TERM...BRS
LONG TERM...BRS
AVIATION...BRS/Haines
MARINE...BRS/Haines