117
FXUS62 KCHS 261907
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
307 PM EDT Wed Jun 26 2024

.SYNOPSIS...
High pressure will remain over the western Atlantic while weak
cold fronts linger near the area through the end of the week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Radar returns from KCLX indicate that afternoon convection has
begun o fire off, mainly along and just west of I-95. Strong to
marginally severe thunderstorms will be possible heading into
this afternoon, with SPC Mesoanalysis indicating around 1500
J/kg of ML CAPE.

At the surface a stationary front will meander across the SC
Upstate. Aloft a larger scale trough will be positioned over the
Great Lakes, with the forecast area in the vicinity of the
southern periphery. Temperatures this afternoon have already
reached into the low 90s across many locations, with dew point
observations in the mid to upper 70s across the coastal
counties. Further inland dew points have been able to mix out,
resulting in observations reporting in the mid to upper 60s. The
Heat Advisory is verifying already across the coastal plain,
with KJZI and KNBC reporting heat index values of 108F. No
changes were made to the areal extent of the Heat Advisory.

Ample instability will be present this afternoon across the
forecast area, however a forcing mechanism will be lacking.
Therefore, afternoon convection will be driven by the inland
pushing sea breeze and any outflow boundaries that develop.
Isolated to scattered showers and thunderstorms will be possible
this afternoon, likely dissipating by sunset. With the
instability in place, a strong to marginally severe thunderstorm
cannot be ruled out.

Tonight: Diurnally driven convection will run its course
through the evening hours. As mentioned, upper level troughiness
will edge into the southeast region through the course of the
night with enhanced QG-forcing for ascent working across the
Appalachians and into the western Carolinas. It does appear at
this juncture that any associated shower activity will remain
well upstream through the night and plan to maintain a dry
forecast. Low temperatures once again will only dip into the
middle 70s to around 80.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday: Passing shortwave energy across the Virginia Tidewater
will help drive a weak cold front south through North Carolina and
into South Carolina during the day Thursday. This front coupled with
possible sea breeze interactions will support the development of
scattered showers/tstms during the afternoon and evening hours.
Model soundings within the warm sector are not overly unstable for
late June despite strong surface heating and high surface dewpoints.
This is likely due to some weak subsidence/mid-level warming noted
around 550 hPa. Still, with modest forcing aloft with approaching
shortwave energy, strong low-level lapse rates and modest mixed-
layered instability in place, there are more than enough mechanisms
in place to support the genesis of convection.

Locally, the greatest coverage looks to occur in the vicinity of the
Charleston Tri-County region during the mid-late afternoon hours
near the intersection of the sea breeze with the southward moving
cold front. Additional, more airmass driven convection, appears
likely to develop over interior Southeast Georgia which will spread
east into far southern South Carolina as the afternoon/evening
progresses. A belt of 25-30 kt of 0-6km bulk shear is forecast to
drop south in tandem with the approaching front. This may help aid
in the development of some stronger, possibly more organized
convective clusters during the late afternoon/early evening hours,
mainly centered from Colleton County and points north, including the
Charleston Metro Area. However, with DCAPE averaging about 1200 J/kg
south of the front, there will be a risk for a few strong to severe
tstms just about anywhere across Southeast South Carolina and
Southeast Georgia, especially where updrafts can become enhanced
near mesoscale boundary collisions. Highs in the mid-upper 90s away
from the coast coupled with dewpoints in the mid-upper 70s east of I-
95 will support heat indices of 108-112. Another Heat Advisory could
be needed for areas along/east of I-95. Showers/tstms will diminish
overnight with a risk for at least isolated convection lingering
through daybreak Friday. Lows will range from the lower-mid 70s well
inland to around 80 at the beaches.

Friday and Saturday: Weak troughing aloft will be replaced by
building subtropical ridging for both Friday and Saturday. The focus
for convection looks ill-defined and the convective character looks
to mostly airmass driven with K-indices running in the mid 30s.
Models appear be struggling with the timing/placement convection and
forecast soundings depict warming mid-level temperatures as
subsidence builds aloft. Pops were limited to 40% both afternoons
given this trend, mainly concentrated ahead of the inland moving
sea breeze. Convection will die out during the evening with the
strongest low-level convergence shifting closer to the Gulf Stream.
Highs both days will reach into the mid-upper 90s away from the
coast with dewpoints holding in the mid-upper 70s east of I-95. Heat
indices could peak above 108 both afternoons and Heat Advisories may
be needed. Lows Saturday morning will range from the lower-mid 70s
inland to around 80 at the beaches.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Sunday still looks be heavily influence by broad subsidence aloft
which may limit convection a bit. Pops were limited to chance for
now and mostly concentrated inland of the sea breeze. A more typical
summer convective pattern will take shape as next week approaches.
Broad troughing looks to develop by Monday which could help enhanced
diurnal convection Monday into Tuesday. There are considerable
mesoscale and timing details to be worked out, so pops were capped
at chance for now which is considerably lower than the more
aggressive 16/13z NBM. Sunday looks to be the last day for excessive
heat with heat indices 108+ mainly confined to areas long/east of I-
95 as highs warm into the mid-upper 90s away from the coast. Heat
Advisories may be needed. Somewhat cooler conditions will occur
Monday into Tuesday with highs only peaking in the lower-mid 90s
away from the coast as a weak cold front approaches. Lows each night
will drop into the lower-mid 70s inland with upper 70s/near 80 at
the beaches.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
KCHS/KJZI: Scattered showers and thunderstorms are possible
this afternoon into early evening. However, indications are that
most of the activity will occur a bit inland from the
Charleston County coast and may not impact the terminals. Still
too much uncertainty to include an explicit mention in the
terminal forecasts, but will carry VCSH at KCHS during the
afternoon.

KSAV: A similar story, with showers and thunderstorms possible
this afternoon into early evening. Recent guidance trends
suggest KSAV will have the higher probabilities for showers and
storms. 18Z terminal forecast will carry VCTS at the terminal
during the mid to late afternoon period.

Extended Aviation Outlook: Flight restrictions in scattered
showers/tstms could occur at any of the three terminals each
afternoon and evening.

&&

.MARINE...
Persistent southerly flow will linger across the coastal waters
through tonight, generally 10 to 15 knots with some gusts to
around 20 knots. Seas 2 to 3 feet through today building to 2 to
4 feet tonight.

Thursday through Sunday: Southerly wind regime will persist through
the period with typical sea breeze enhancements likely along the
land/sea interface and Charleston Harbor with the afternoon sea
breezes. Winds look to hold below 15 kt with seas 3 ft or less.

Rip Currents: A lingering 2 ft, 9 second swell coupled with some
astronomical influences and typical sea breeze enhancements along
the beaches support a moderate risk for rip currents for all beaches
both Thursday and Friday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 7 PM EDT this evening for GAZ101-116>119-
     138>141.
SC...Heat Advisory until 7 PM EDT this evening for SCZ043>045-
     047>052.
MARINE...None.

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...