Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 261437
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1037 AM EDT Tue Mar 26 2024

.SYNOPSIS...
High pressure will move off the coast today. A storm system
will impact the area Wednesday into Thursday, followed by high
pressure through early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: Aloft, the axis of a broad ridge will become positioned
further offshore this afternoon 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 late morning
and afternoon. The front could eventually nudge a band of convection
toward inland tier counties late day, but the vast majority of
the local area is expected to remain rain-free. Isentropic ascent
and southeast sfc winds should maintain partly cloudy to cloudy
conditions across many areas through the afternoon, 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 /15Z TUESDAY THROUGH SATURDAY/...
KCHS/KJZI: There will be MVFR ceilings at both sites this
morning as the low level inversion has strengthened and trapped
considerable moisture underneath. There will even be a few
sprinkles from off the ocean. But no impacts would occur. VFR
returns late this morning into tonight, but some MVFR ceilings
are again possible late as the flow turns southerly ahead of an
approaching cold front and wave of low pressure. 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: VFR through much of the forecast period, with gusty SE
winds at least near 20 kt from late morning into the early
evening. A band of showers and a few TSRA will approach the
terminal from the west late tonight. For now we show VCSH and
MVFR ceilings, but worse conditions are possible.

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...
Today 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 veer from the 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. Seas will be slow to subside, but eventually support Small
Craft Advisories to end across nearshore SC waters south of the
Edisto and across nearshore GA waters. Nearshore waters along
Charleston County will follow late afternoon as seas subside to
5 ft or less. The Georgia waters out 20-60 nm will still have 6
or 7 foot seas tonight, so a Small Craft Advisory will persist
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 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...DPB
SHORT TERM...JRL
LONG TERM...JRL
AVIATION...
MARINE...DPB


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