Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 261952
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
352 PM EDT Tue Mar 26 2024

.SYNOPSIS...
A slow moving cold front and area of low pressure will impact
the area Wednesday into Thursday. High pressure will prevail
Friday into nearly next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Tonight: Aloft, a broad ridge will shift further south and offshore
this evening while a large longwave trough progresses across the
Midwest and Deep South. At the sfc, high pressure will erode and
shift offshore this evening well ahead of a cold front approaching
from the west late. Considerable moisture advection will transpire
ahead of the upstream front, leading to PWATs increasing above
1.5 inches locally by late evening, and this could lead to a few
showers entering western most zones within a few hours of sunset,
before chances increase overnight as the region becomes fully
embedded in a pre-frontal warm air advection regime and isentropic
ascent. However, the precip process will be slow to spread east
toward the coast late as the approaching front becomes more
aligned with the flow aloft. Nevertheless, the environment will
remain supportive of numerous showers along with a few embedded
thunderstorms west of I-95 late where MUCAPE approaches 500-750
J/kg a few hours prior to daybreak. At this time, concerns for
strong and/or isolated severe weather remains low, but rainfall
totals between 1/4 to 1/2 inch are possible with showers/thunderstorms
well inland, and could approach 1 inch for locations experiencing
a thunderstorm before daybreak. Overnight lows will remain mild
within the warm-air advection regime, generally ranging in the
low-mid 60s.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: A cold front will approach and eventually briefly stall
over the area Wednesday as phased shortwave energy over the Central
Plains ejects out into the Great Lakes Region. Models are finally
showing a bit more consistency of briefly stalling out the front
near the I-95 corridor Wednesday afternoon into Wednesday night as
frontal wave begins to develop over the northeast Gulf of Mexico.
This is in response to yet another shortwave ejecting out of Texas
as it rounds the base of the longwave trough centered the central
third of the country. A combination of modest warm air advection,
DPVA and influences from the right entrance region of a 140 kt jet
streak embedded in the subtropical jet will yield about a 9 to 12-hr
window of intense, deep-layered vertical velocities over the local
area. This period of synoptic lift is well reflected in the various
model time sections. This should result in a fairly widespread rain
shield of light to moderate rainfall encompassing much of Southeast
South Carolina and Southeast Georgia, from mainly late Wednesday
afternoon into the early morning hours Thursday as the frontal waves
passes through. This will also be when the strongest forcing becomes
aligned with highest deep-layered moisture with some additional
contributions from some weak surface-based instability.

Flash flooding is not still not a major concern, but some minor
flooding of low-lying and poor drainage areas can not be ruled out,
especially where some embedded tstms occur. Categorical pops around
80-90% look on track. Highs will warm into the lower-mid 70s with
overnight lows dropping into the mid-upper 50s, except near 60 at
the beaches and Downtown Charleston.

Thursday: The steadier rains will quickly come to an end Thursday
morning as the frontal wave exits to the North Carolina Outer Banks
and the front finally pushes offshore. A few showers with the upper
trough itself could impact mainly southern South Carolina, possibly
as far south as the I-16 corridor in Southeast Georgia, during the
afternoon, but these should not contribute much to the storm total
QPF of 1-2". It will become breezy at times Thursday afternoon with
the onset of post-frontal cold air advection. Gusts could be near 30
mph at times. It will be a bit cooler with highs only reaching the
upper 60s/lower 70s with overnight lows Friday morning dropping into
the lower 40s well inland with lower 50s at the beaches.

Friday: Much calmer and drier conditions are expected Friday as high
pressure builds into the region. Highs will warm into the upper
60s/lower 70s. A weak sea breeze could develop along mainly the
Georgia coast late Friday afternoon.

Lake Winds: Gusty northwest winds will develop on Lake Moultrie
Wednesday afternoon and continuing to Wednesday night. Vigorous
mixing is expected over the open lake waters with the onset of post-
frontal cold air advection. Modified soundings support 15-20 kt with
gusts to 25-30 kt. Waves will build to 1-2 ft, mainly over the
central and southeast portions of the lake. A Lake Wind Advisory
will likely be needed.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Broad ridging aloft will dominate for much of the period with high
pressure prevailing at the surface. Temperatures will steadily
moderate through the period. Highs well into the 80s will be common
early next week. There is a slight chance that a backdoor cold front
could drop into the area Tuesday bringing a risk for some showers,
but there is much uncertainty on how far south the front given the
northwest flow aloft.

&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
VFR conditions are expected at CHS/JZI/SAV terminals this afternoon
and into early evening. MVFR cigs should then develop across all
terminals overnight, likely arriving by 08Z Wednesday, and possibly
a few hours prior. A band of showers (possibly a few embedded
thunderstorms) is expected to shift across the area late tonight and
into Wednesday morning, which will likely favor MVFR cigs/vsbys to
continue into late morning/early afternoon Wednesday. IFR conditions
are possible at the terminals with showers and/or a thunderstorm
Wednesday morning, but confidence is too low to include in the
latest TAF issuance.

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

&&

.MARINE...
Tonight: High pressure will erode and/or shift further offshore in
advance of a cold front approaching the region late, setting up
winds that gradually veer from east-southeast to south late with
speeds no higher than 15-20 kt across northern SC and Charleston
Harbor waters early evening. Seas will be slow to subside, but
will generally range between 3-5 ft across nearshore waters and
5-7 ft across offshore Georgia waters overnight. A Small Craft
Advisory will continue across offshore Georgia waters through
the night.

Wednesday through Sunday: The primary concern centers on Thursday
into early Friday morning as low pressure pulls away from the region
and a cold front pushes offshore. Northwest winds will surge to 15-
25 kt with gusts 25-30 kt by Thursday afternoon/evening with the
onset of modest post-frontal cold air advection. Winds will begin to
diminish early Friday as cold air advection begins to wane and high
pressure builds in from the west. Seas will peak 4-6 ft nearshore
waters within 20 NM of the coast and 5-7 ft over the Georgia
offshore waters 20-60 NM offshore. Small Craft Advisories will
likely be needed for all nearshore legs and Charleston Harbor. An
advisory is already in place for the Georgia offshore leg 20-60 NM
out.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 6 AM EDT Friday for AMZ374.

&&

$$

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


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