Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 261812
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
212 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 /THROUGH TONIGHT/...
This Afternoon: Aloft, the axis of a broad ridge will become
positioned further offshore while a large longwave trough traverses
east over the Central United States and enters the Midwest and Deep
South regions. At the sfc, a high pressure wedge extending across
the area will gradually erode and/or shift offshore in advance of a
cold front tracking across the Deep South. The front could
eventually nudge a band of convection toward inland tier counties by
the evening, but the vast majority of the local area should remain
rain-free through sunset. Isentropic ascent and east/southeast sfc
winds should maintain partly cloudy to cloudy conditions across many
areas, but a favorable warm air advection regime within a southwest
flow aloft will help temps become noticeably warmer than the
previous day regardless of strong sfc heating, especially across
southern areas. In general, afternoon highs should peak in the low-
mid 70s across southeast South Carolina to upper 70s/around 80 away
from the coast across southeast Georgia (warmest near the Altamaha
River).

Tonight: Considerable advection of moisture transpires ahead of
the upstream cold front that is near the central and southern
Appalachians late. Pwat as a result climbs above 1.5 inches
overnight. There is also the possibility of a weak wave of low
pressure along a stationary front or trough closer to the
immediate counties. Rain chances will begin to climb after
midnight, as the region becomes more fully embedded in the zone
of pre-frontal warm air advection/isentropic ascent, allowing
for a broad band of convective rains associated with the
approaching cold front drawing closer. This will be a very slow
process though as the front starts to become aligned with the
flow aloft. Consensus of the models is for a Theta-E ridge to
move into places near and west of I-95, which is also where we
find the best upward omega, and closer proximity to upper
divergence associated with a strong jet aloft.

Evening convection will wane prior to midnight as we transition
from diurnal heating to a nocturnal environment. We then have
PoPs as high as 60-80% from Allendale to Tattnall County,
although higher PoPs will likely be required. PoPs are tapered
down to 30-40% further east, including Charleston, Beaufort, and
Savannah. There`s an axis of MLCAPE as high as 500-750 J/kg
across the region, so we have included mention of at least
isolated t-storms. No risk of severe weather as of this time.
QPF will be mainly 1/4 inch or less, although a quick 1 inch or
so can occur in any t-storms, especially far inland.

It`ll be a warm night for late March given continued warm
advection, plenty of clouds, and higher dew points within a
southeast and south flow. We currently have 60-65 degrees for
low temperatures, which is a good 10-15 degrees above climo.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
A surface front will remain stalled north to south across the
area Wednesday and Wednesday night while the upper trough sits
to our west. Extensive upper shortwave energy is forecast to
move through the area during this time. Meanwhile, 30-40 kt
southerly 850-700 mb flow will bring 1.7-1.8" PWs into the area.
A small amount of instability could develop Wednesday afternoon
with CAPEs around 500 J/kg. Numerous showers and isolated
thunderstorms are expected to develop across the western half of
the area Wednesday morning, then shift east. A weak surface wave
is forecast to move up the coast Wednesday night, likely
bringing widespread showers and a few thunderstorms to the
majority of the forecast area. The greatest QPF is expected to
occur Wednesday night, where 1-1.5" is possible.

The upper trough will swing through on Thursday. Despite the
surface low being northeast of the area, most of the guidance
indicates the cold conveyor belt will result in some wrap around
precipitation during the day Thursday, especially across
southern SC. The deep moisture will finally scour out by late
Thursday afternoon when we should see rapid clearing. Cold air
advection during the day will result in breezy NNW winds which
could necessitate a Lake Wind Advisory for 25 kt gusts on Lake
Moultrie.

Friday should be dry and sunny with highs a degree or two either
side of 70.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
Deep layered ridging with a low-level warm advection regime will
produce dry weather and well above normal temperatures this
weekend through early next week. Highs in the upper 70s
Saturday, then low to mid 80s Sunday and Monday.

&&

.AVIATION /18Z 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 through Thursday. Occasional vsby
restrictions possible in showers/tstms, especially Wednesday and
Wednesday night.

&&

.MARINE...
This Afternoon and 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 to southeast
this afternoon. In general wind speeds should gradually weaken
during the day, peaking no higher than 15-20 kt across northern SC
and Charleston Harbor waters early afternoon. 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. Winds will
continue to veer overnight, becoming more southerly late as the
front approaches inland, but are expected to remain at or below 15
kt. Further offshore, seas will remain elevated, ranging between 5-7
ft. Thus, a Small Craft Advisory will continue across offshore
Georgia waters through the night.

Southerly flow will continue Wednesday and Wednesday night.
Although wind speeds will have diminished, 6 ft seas likely to
continue on the offshore GA waters. Winds turn to the NW and
strengthen on Thursday after a cold front moves through. We`ll
likely need Small Craft Advisories for the Charleston nearshore
and GA offshore waters Thursday into Friday due to a combination
of 25 kt wind gusts and 6 ft seas.

&&

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

&&

$$

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


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