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653
FXUS62 KCHS 182003
AFDCHS

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

.SYNOPSIS...
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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.
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&&

.NEAR TERM /THROUGH SUNDAY/...
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Late this afternoon, KCLX detected a ragged band of showers across
the forecast area. Based on radar trends and stable environment,
these showers should gradually dissipate through the rest of this
afternoon. Isolated to scattered convection will remain possible
this evening through overnight, little additional rainfall expected.
Late tonight, high clouds are expected to decrease from west to east
across the region. Given the wet ground and light winds, patchy fog
or ground fog may develop inland late tonight. Low temperatures are
forecast to range from the mid 60s inland to near 70 along the
coast.
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&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/...
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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.
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&&

.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 /20Z SATURDAY THROUGH THURSDAY/...
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KCHS/KJZI/SAV: KCLX detected stratiform across the terminals,
occasional lightning strikes observed near KSAV. It is possible
that MVFR visibility during -TSRA may remain over KSAV into the
mid-afternoon. Otherwise, KCHS and KJZI should see showers
remain over the terminal into the mid to late afternoon. The
challenge overnight will be the potential development of fog
and/or MVFR ceilings. At this time, only the KSAV will indicated
MVFR fog developing at 8Z and remaining through the rest of the
night. MOS and forecast soundings indicate that MVFR stratus
will develop at daybreak at each terminal, remaining through
Sunday morning.

Sunday: Widespread showers/storms expected Sunday afternoon. These
storms will move very slowly and produce heavy rainfall, with the
potential for prolonged periods of vis restrictions in heavy
rainfall in the afternoon.

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

.MARINE...
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The sfc pattern should support south winds between 10 to 15 kts
tonight. Wave heights are forecast to gradually build to 2-3 ft by
late tonight.

Sunday through mid-week: 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...
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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.
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&&

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

&&

$$

NEAR TERM...NED
SHORT TERM...CEB
LONG TERM...CEB
AVIATION...CEB/NED
MARINE...CEB/NED