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216
FXUS62 KCHS 172241
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
641 PM EDT Fri May 17 2024

.SYNOPSIS...
A storm system will bring impacts to our area this weekend.
High pressure returns to our region next week.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Poor lapse rates, a Normalized CAPE less than 1 unit, and
limited MLCAPE have kept convection in check, with mainly just
isolated to scattered showers. The closest t-storms as of early
evening are in southwest Georgia. As the evening progresses, mid
level lapse rates get a little better, MLCAPE increases to as
much as 500-1000 J/kg, and with deep shear of 40-50 kt, there
will be an increase in convection. Recent HRRR guidance does
show some potential fro strong or severe t-storms over Long and
McIntosh County during the mid and late evening. But the Warn on
Forecast (WoF) keeps the better chances to the south of the
Altamaha River. Due to Supercell Composite values as high as
2-4, we`ll maintain mention of isolated severe storms with maybe
a tornado in the Hazardous Weather Outlook for Long and McIntosh
County.

There are indications that additional activity could attempt to
move in from the west and southwest closer to daybreak. But this
scenario will be re-evaluated with the next update.

Depending upon how much rain occurs, there could be some stratus
developing and building down late, as per the LAMP and to some
extent the HREF. Even so, geostrophic winds look a little too
high for any serious fog concerns.

Low temperatures will be well above normal given the elevated
dew points and extensive cloud cover.
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&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Much of this period is expected to be the most active for the entire
forecast period through the next work week. Models show an upper
level trough over the lower MS River Valley early Saturday, moving
eastward toward the forecast area through Sunday. Conditions look
the most favorable for showers/thunderstorms later Saturday
afternoon through Sunday. Peak values of CAPE and bulk shear will be
later Saturday afternoon and Saturday evening, which is the main
time frame that the SPC has our entire region in a SLT Risk for
severe storms. Have kept high likely/low end categorical PoPs for
much of the area on Saturday and Saturday evening, chance Saturday
night, and then likely again Sunday. The threat for any severe
storms looks too low to mention for Sunday due to a significant
decrease in CAPE, despite the passage of a surface cold front and
the presence of the upper level trough. By later Sunday night and
Monday, the upper trough axis will move offshore, allowing a cold
front to push south of the area. High pressure builds in from
the northwest Sunday night and Monday, which will bring slightly
cooler and drier conditions.

Temperatures above normal Saturday, near normal Sunday and possibly
a tad below normal behind the cold front on Monday.

Heavy Rainfall Potential: Blended models solutions continue to point
toward later Saturday afternoon and evening for the most likely
window for locally heavy rainfall. The area with the highest chance
for heavy rainfall appears to be our coastal counties, especially
from the Charleston Tri-county region, southward to the Savannah
River. However, there continues to be uncertainty in the exact
placement of the heavy rainfall, since localized boundaries produced
by convection/thunderstorms will likely dictate where the heaviest
rainfall occurs. Thunderstorm induced boundaries could collide with
a weak seabreeze close to the coast Saturday afternoon, which is why
we are leaning toward higher chances for the heaviest rainfall to be
over our coastal counties.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
This period looks to be much quieter, with little/no chances for any
significant rainfall and temperatures above normal. Another cold
front may impact the area later Thursday and Friday with at least
slight chances for showers/thunderstorms. However, the timing of
this front and whether or not there will be sufficient deep layer
moisture to support precipitation remains uncertain. Temperatures
expected to be above normal during this period, especially by
Thursday and Friday as a deep layer ridge builds to the south-
southwest of the area, keeping our region under low level west-
southwest flow.

&&

.AVIATION /23Z SATURDAY THROUGH WEDNESDAY/...
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Prior to the 18Z TAFs, KCLX detected scattered showers
streaming across SE GA, with showers passing over and near KSAV.
Showers and thunderstorms should gradually increase across SE
GA through mid-evening. The KSAV TAF will feature a TEMPO
between 0-3Z for VRB10G15kt during TSRA. KCHS and KJZI may see
passing showers this evening into the late night hours. MOS and
forecast soundings indicate that MVFR ceilings are expected to
develop over the terminals late tonight remaining into mid
Saturday morning. Conditions are expected to become VFR by 14Z
Saturday.

Extended Aviation Outlook: Saturday through Sunday: Periods of
showers and thunderstorms are expected with brief flight
restrictions possible, especially later Saturday afternoon and
evening. Isolated to scattered strong to severe storms will be
possible Saturday afternoon and evening.

Sunday night through Wednesday: VFR expected to prevail.
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&&

.MARINE...
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The surface pattern will support south winds between 10 to 15
kts, with gusts around 20 kts 15 nm and beyond. Wave heights are
forecast to gradually build to 2-3 ft by late tonight. A
cluster of strong thunderstorms may push off the Georgia coast
late this evening. It is possible that a Special Marine Warning
or Marine Weather Statement could be issued later tonight.

No highlights are expected through the period. The waters will
remain under the influence of a ridge of high pressure well to the
southeast and lower pressure well inland, to the northwest. This
will keep southwest winds of 15 knots or less and seas generally 2
to 4 feet through Sunday. A cold front is expected to push through
the waters during the day on Sunday. Behind this front, winds will
veer to north-northwest and increase to 15 to 20 knots. Seas
building to 3 to 5 feet.  The increased winds/seas are not expected
to persist long. They should begin to subside a bit by later Monday
as winds become more northeast at 15 knots or less, with seas 2 to 4
feet Monday night through Wednesday.
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&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

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