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783
FXUS62 KCHS 182208
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
608 PM EDT Sat May 18 2024

.SYNOPSIS...
Unsettled weather continues ahead of a cold front that will
cross the area later Sunday. High pressure then dominates
through much of the coming week, with another storm system
potentially impacting the area late week.

&&

.NEAR TERM /THROUGH SUNDAY/...
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Earlier shower/tstm activity has ended. The risk for a few
showers will persist overnight, possibly increasing a bit over
the far southern areas Darien later this evening as a weak
perturbation passes by to the south. Pops were lowered to 20-30%
for the early evening update. Any mention of tstms were also
removed as much of the area has been worked over from earlier
convection. Some patchy fog could develop inland early Sunday,
but elevated winds just of the surface could limit coverage and
promote more in the way of stratus. Lows from the mid 60s well
inland to the lower 70s at the beaches and Downtown Charleston
are on track.
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&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
Sunday: A positively tilted mid-level trough will be over the
Southeast U.S. in the morning. It`ll slowly shift offshore into the
evening and overnight. The dominate cold front will be stretched
along the SC coast and the I-16 corridor in the morning with ridging
building in from the north and west behind it. This diffuse front
may get hung up in the sea breeze if it is still nearby come midday,
providing enhanced initiation for convection.

The main story for Sunday has become the clear threat for heavy
rainfall. Deep moisture will remain in place across the region with
PWATs in the 1.5-2.0" range. These values are above the 90% mark per
SPC sounding climatology for CHS. They`re also about 2 standard
deviations above normal per NAEFS. With all of the moisture and lift
in place, models are in good agreement that widespread showers will
develop with increasing instability come midday. Very slow storm
motions - less than 10 mph - and very high rain rates - perhaps on
the order of 2 to 3 inches per hour - could bring localized rainfall
amounts up to 3-4+ inches over the course of several hours in the
afternoon. The flooding threat will be enhanced for areas that
received 1-2+ inches from Beaufort County to the I-16 corridor and
south on Saturday.

Monday: The mid-levels will consist of a positively tilted trough
just off the Southeast U.S. coast in the morning, and a ridge just
to our west. The ridge will slowly build into our area as time
progresses. At the surface, High pressure centered well to our north
will build down the coast, with it`s southern periphery making its
way into our area. The High will bring drier conditions with skies
becoming mostly sunny/clear. Low-level thickness values support
temperatures in the middle 80s. But we went a little below this due
to the northeasterly surface winds and the expectation that surface
evaporation should limit temperatures. Highs should peak in the
lower 80s. Lows should range from the upper 50s far inland to the
mid 60s closer to the coast.

Tuesday: A positively tilted mid-level trough will be just off the
Southeast U.S. coast in the morning, while a ridge will prevail over
the Southeast U.S. High pressure centered just to our north in the
morning will shift off the Mid-Atlantic Coast as the day progresses.
Though, it`s southern periphery will continue to dominate our
weather. Subsidence will yield dry conditions with mostly sunny
skies. Temperatures should rise to near normal.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Mid-level ridging will be over our region through Wednesday,
followed by southwest flow on Thursday. A weak trough may pass to
our north on Friday. Broad surface High pressure will stretch from
just to our north into the Atlantic Tuesday night into Wednesday.
It`s expected to shift offshore later Thursday. A cold front could
approach from the northwest later Friday, possibly bringing showers
and thunderstorms. Temperatures will be trending higher, reaching
into the 90s by Thursday.

&&

.AVIATION /22Z SATURDAY THROUGH THURSDAY/...
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19/00z TAF Discussion:
VFR this evening with an increased risk for MVFR cigs as
daybreak approaches. There could be a little ground fog that
develops, mainly at KSAV and possibly KJZI, but the best
fog/stratus parameters look to remain to the west of all three
terminals. The risk for showers/tstms will increase during the
day Sunday as a cold front moves through. The best focus for
showers/tstms looks to settle just south of KCHS and impacting
KJZI and KSAV. A TEMPO for TSRA was included from 18-21z at KCHS
to account for some coverage/timing uncertainties. Prevailing
TSRA was mentioned for both KJZI (18-21z) and KSAV (20-00z).
Conditions were limited to MVFR for now with both cigs/vsbys
holding above alternate minimums. However, lower conditions may
eventually be needed as confidence in the timing, placement and
intensity of showers/tstms increases.

Extended Aviation Outlook: VFR.
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&&

.MARINE...
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Tonight: The sfc pattern should support south winds between 10
to 15 kt with seas 2-3 ft.

Sunday through Thursday: A weak cold front nearby will bring
the potential for showers and storms with heavy rainfall and
lightning Sunday afternoon. The cold front will push offshore
later Sunday, with ridging building inland and troughing
persisting well offshore through mid-week. The strongest
gradient will occur on Monday morning, with wind gusts to around
20 kt possible across much of the coastal waters, and seas
increasing to 3-5 ft (in mainly windswell) accordingly. The
gradient then gradually weakens and seas gradually subside as
the inland high becomes more dominate Tuesday and Wednesday.
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&&

.TIDES/COASTAL FLOODING...
The combination of high astronomical tide levels and moderate to
breezy NE winds will bring the potential for elevated tide levels
early next week. Minor flooding is possible with the early evening
high tide Monday mainly along the South Carolina coast.

&&

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

&&

$$