Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 260526
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
126 AM EDT Tue Mar 26 2024

.SYNOPSIS...
High pressure will prevail through early Tuesday. A storm
system will impact the area Wednesday into Thursday, followed
by high pressure into next weekend.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Aloft, a ridge of high pressure over the Southeast will slowly
push offshore overnight well in advance of a large trough
traversing the Central United States. At the surface, a high
pressure wedge extending across the Mid-Atlantic and Southeast
states will hold along with a weak coastal trough lingering off
the Georgia coast. Weak isentropic lift will keep a steady
stream of strato-cumulus moving onshore through the night. A
swath of higher Theta-E air coinciding with some low level
moisture convergence from off the Atlantic could generate a few
very light showers or sprinkles across parts of Beaufort,
Colleton and Charleston County.

Temps will remain slightly more mild than the previous night
with weak warm air advection in place, surface winds turning
easterly and low-lvl moisture favoring nearly mostly cloudy
skies through the night. Overnight lows will fall into the lower
and middle 50s across most communities inland, with upper 50s to
near 60 closer to the coast. With warm air advection ramping up
early morning, it is possible for locations to hit their low
around 3-5am, before remaining steady thereafter or even
slightly increasing until sunrise.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
Tuesday: Broad H5 ridging along the Eastern Seaboard will quickly
breakdown as a large longwave trough over the central and western
portion of the country nudges east. A potent southern stream
shortwave will help drive a cold front to the east as it begins to
eject out of the Southern Plains in response to its phasing with a
northern stream shortwave digging into the Northern Plains. At the
surface, the high pressure wedge will shift offshore into the
Atlantic during the day. The increasing southerly flow will likely
maintain some degree of stratocumulus moving inland from off the
Atlantic as an extensive high cirrus deck persists over the
Southeast States. This will yield mostly cloudy to cloudy conditions
into Tuesday night as the cold front to the west draws closer. Highs
look to warm into the lower-mid 70s over Southeast South Carolina
with mid-upper 70s over Southeast Georgia, except cooler at the
beaches. Lows Tuesday night will range from the lower-mid 60s with
a few upper 50s in the Francis Marion National Forest.

A few showers, mostly aided by pre-frontal warm air advection-
isentropic ascent, could propagate into far interior portions of
Southeast Georgia during the afternoon. Similarly, a rouge shower or
two could move inland from off the Atlantic, but models are
typically overdone with generating precipitation over the
Atlantic in onshore flow. Overall, expect most locations will
remain rain- free through sunset. Rain chances will begin to
slowly ramp up late Tuesday night as the region becomes more
fully embedded in the zone of pre-frontal warm air
advection/isentropic ascent and a broad band of rain associated
with the approaching cold front draws ever closer. It is around
this time that the cold front begins to slow down as it become
increasingly parallel to the the flow aloft. How quickly the
front slow down will have an influence on how much coverage of
rain will spread east. For now, mentionable pops were limited to
areas along/west of I-95 with the highest pops (up to 60%) were
limited to the Reidsville-Sylvania-Metter-Allendale corridor.
Further adjustments will likely be needed.

Wednesday and Thursday: This looks to be the wettest period of the
next seven days. The aforementioned cold front looks to stall over
Southeast South Carolina and Southeast Georgia on Wednesday as a
frontal wave begins to develop along the front and moves northeast
along it. This is in response to the large, mostly phased mid-level
trough nudging east out of the Plains. Deep-layered forcing looks to
peak Wednesday night into Thursday morning as a piece of negatively-
tilted vorticity propagates through the area as it rounds the base
of mean upper trough. PWATs >1.50 inches, a moist, southerly flow
fed by a 30-40 kt 850 hPa low-level jet and even some hint at some
surface based instability will support a broad region of light to
moderate rainfall. While a general wet trend is noted, there remains
some model uncertainties with respect to timing as much will depend
on where the front stalls and the corresponding frontal low tracks.
For now, pops were limited to 50-70% for Wednesday (highest west of
I-95) and 80% Wednesday night with 40-70% Thursday morning (highest
along the middle South Carolina coast). Similar to Tuesday, further
adjustments will likely be needed as models begin to better resolve
front`s timing. A general 1-2" rainfall looks reasonable for the
area. Flash flooding does not appear likely, but some minor flooding
of low-lying and poor drainage areas can not be completely ruled out.

Highs Wednesday will warm into the lower-mid 70s, then cool to the
upper 60s to near 70 by Thursday as low pressure pulls away and a
cooler and drier airmass settles into the region. Lows Thursday
morning will drop into the mid-upper 50s inland to around 60 at the
beaches.

Lake Winds: Winds will increase on Lake Moultrie Thursday in a post
frontal cold air advection regime. Expect northwest winds of 15-20
kt with gusts around 25 kt. The 25/13z NBM shows >80% chance for
wind gusts exceeding 25 kt on the open lake waters, mainly Thursday
afternoon. Waves will build 1-2 ft, mainly over the central and
southeast portions of the lake.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Mostly quiet weather will dominate through the period with high
pressure centered across the Southeast United States late week
gradually sliding south and offshore through the weekend. Expect
moderating temperatures to unfold locally with afternoon highs
peaking into the lower 80s away from the coast by Sunday,
followed by another warm day in the lower 80s on Monday.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI: There could be a period of MVFR ceilings at both
sites early this morning as the low level inversion strengthens
and traps additional moisture underneath. Otherwise VFR through
06Z Wednesday. Maybe a few sprinkles or even a very light
shower from off the ocean early this morning. But no impacts
would occur. E and SE winds remain somewhat elevated through
the entire period, with gusty winds at times at least into the
15-20 kt range this afternoon and early evening.

KSAV: Based on observations and the HREF, it appears that the
MVFR ceilings have shifted inland of the terminal. We`ll still
need to monitor for sub-VFR ceilings at times through through
the morning with the flow off the ocean. Otherwise, VFR will
prevail through 06Z Wednesday, with gusty SE winds at least near
20 kt from late morning into the early evening.

Extended Aviation Outlook: MVFR ceilings with possible periods of
IFR expected late Tuesday night through Thursday. Occasional vsby
restrictions possible in showers/tstms, especially Wednesday and
Wednesday night.

&&

.MARINE...
Overnight: A wedge of high pressure extending across the
Southeast will favor an enhanced pressure gradient across the
region through the first half of the night, before gradually
retreating north late. Small Craft Advisories will be ongoing
through the night across all local waters outside the Charleston
Harbor, although east-northeast winds gusting up to 20-25 kt
will gradually veer and weaken to 15-20 kt. Seas will also
slowly subside, but will remain between 4-6 ft across nearshore
waters and 6-8 ft across offshore Georgia waters after midnight.

Tuesday: East to southeast winds will prevail as high pressure shifts
offshore of the U.S. East Coast. Speeds will generally remain less
than 15 kt. Seas will start off the day in the 4-6 ft range with 20
NM, but should drop below the Small Craft Advisory 6-foot sea
criteria later in the day. Over the Georgia offshore water, seas
will hold into the 5-7 ft range into Tuesday night. Small Craft
Advisories remain in effect.

Wednesday through Saturday: A broad, southerly wind regime will
prevail Wednesday as high pressure shifts farther offshore a cold
front approaches from the west. The front and an associated area of
low pressure will exit the coast Thursday. Gusty, northwest winds
will occur behind the front Thursday into early Friday within a
period of post-frontal cold air advection. Winds will reach 15-25
with gusts to 30 kt, so Small Craft Advisories will likely be
needed. Seas will peak 4-6 ft over the nearshore waters within 20 NM
and 5-7 ft over the Georgia offshore waters 20-60 NM.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 6 PM EDT this evening for AMZ350.
     Small Craft Advisory until noon EDT today for AMZ352-354.
     Small Craft Advisory until 6 AM EDT Friday for AMZ374.

&&

$$

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


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