Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 302347
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
647 PM EST Mon Jan 30 2023

.SYNOPSIS...
A series of weak fronts will impact the region through
mid-week. A stronger storm system will affect the area Thursday
into Friday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Early this evening: Radar imagery shows that the last of the
rain is currently moving across southeast Georgia, south of the
weak front draped across the area. This area along and south of
I-16, actually saw a good bit of sun today and temperatures
warmed at least into the mid 70s. SPC Mesoanalysis even shows
500 J/kg of MLCAPE, and lightning data has shown a few in-cloud
flashes. Now that we are past sunset, these showers will
continue to weaken and dissipate. The main forecast issue
overnight will be fog potential. Widespread low stratus is
already ongoing on the cool side of the boundary and will
continue to spread southward. Conditions should be supportive
with very weak surface flow, plentiful moisture and existing
stratus that appears poised to build down through the overnight.
We have maintained the mention of areas of fog, and there
appears to be a growing likelihood that we will need Dense Fog
Advisories for much of the area at some point. We will continue
to monitor over the next few hours and see how things evolve.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: Morning low clouds/fog will linger through mid-
morning. Zonal flow will remain in place aloft as subtropical
ridging holds firm over Cuba. A weak cold front will stall over
the area Tuesday. A few showers could develop in the vicinity of
the boundary as weak warm air advection/isentropic ascent along
the 295-305K surfaces persists. Major rainfall is unlikely with
only a few hundredths likely to fall where showers occur. Pops
20-30% look reasonable for most areas. Warm/moist conditions
will hold with highs warming into the upper 60s to mid 70s,
warmest south of the I-16 corridor in Southeast Georgia. The
stationary front will washout overnight, but increasing flow in
the 1000-925 hPa layer ahead of yet another front will likely
help to enhance isentropic forcing as weak warm air advection.
Guidance shows a solid uptick in rain chances overnight and pops
have been increased to 30-40% to reflect this. Another round of
low clouds and possibly some fog due to stratus build-down
could occur, but widespread dense fog is not currently expected
due to increasing boundary layer winds. Patchy fog will be
introduced to trend. It will be a somewhat warm and humid night
with the area fully embedded in the pre-frontal warm sector.
Lows will only drop into the mid-upper 50s which is about 15-20
degrees above normal.

Wednesday: A cold front will drop south through the area
Wednesday as high pressure begins to wedge down from the north.
Guidance is fairly consistent in keeping the main corridor of
channeled vorticity displaced well to the north coincident with
the 500 hPa jet, so rain chances will remain somewhat limited
with the lack of any meaningful deep layered UVVs. Weak
isentropic forcing atop the developing wedge will keep a risk
for isolated to perhaps scattered showers in place, but
significant rainfall is unlikely. Highs Wednesday afternoon will
be closely tied to how quickly the wedge can expand south.
Highs look to warm into the lower-mid 60s north of the I-26
corridor to the upper 60s/lower 70s elsewhere, but confidence in
this is only moderate at best given the wedge front could drive
south quicker than expected. Overnight, the wedge will begin to
steadily erode as the wedge front begins to lift north as a
warm front. This is in response to cyclogenesis occurring along
an approaching cold front as a potent shortwave digs across the
Southern Plains. There will be a risk for isolated to scattered
showers impacting the area as the warm front lifts north. Lows
will range from the upper 40s/lower 50s across northern areas to
the mid-upper 50s across the south. If the warm front sharpens
more than expected, temperatures could rise late.

Thursday: The southern stream shortwave moving across the
Southern Plains will gradually phase with secondary shortwave
energy propagating over the Great Lakes Thursday night. Strong
forcing ahead of this mean trough coupled with a high theta-e
airmass in place across much of Southeast U.S. will likely
support a large swath of moderate to locally heavy rains
extending from the Deep South into the Virginia Tidewater. Most
of this activity will likely remain west of the local area
through the day, only approaching the far western zones closer
to sunset. However, a few showers could still occur in the
vicinity of the retreating wedge/warm front across northern
areas through the day. Highs will range from the upper 50s/lower
60s near the Santee River (near the retreating wedge/warm
front) to mid-upper 60s over southern South Carolina with lower-
mid 70s across Southeast Georgia.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A well-defined frontal band of moderate to locally heavy rain
will push through the area Thursday night into Friday as a cold
front works its way offshore Friday morning. Pre-frontal
instability looks minimal and with the front taking on more of
an anafrontal structure, it appears the chances for tstms is
minimal given most of the rain will occur along/behind the
frontal surface. Given the anafront structure, it may take much
of the daytime hours Friday for the rain to finally clear the
coast. Freezing temperatures are expected across the far
interior Friday night, but any lingering showers should be
offshore prior to the arrival of any risk for p- type issues. A
coastal trough could bring another round of showers Saturday
night into Sunday before another cold front clears the coast
Monday. Temperatures will return to more seasonal levels for
much of the extended period.

&&

.AVIATION /00Z TUESDAY THROUGH SATURDAY/...
The 00z TAF period begins with at least MVFR conditions
everywhere across the forecast area, and much of the area is
under IFR conditions. It might take a couple of hours for IFR
ceilings to really settle in at the terminals, but once they do
they will remain through the rest of the overnight and likely
most of the morning. In fact, conditions appear quite supportive
of stratus building down and helping to produce dense fog later
tonight. The TAF`s feature 1/2SM visibilities in fog beginning
around 05-07z and continuing through mid morning. An improvement
to MVFR isn`t likely until midday, and it is possible conditions
will remain sub-VFR through the end of the forecast period.
Isolated showers will be possible as early as mid morning
Tuesday, but the chances of direct impacts are too low to
include explicitly in the forecast at this point.

Extended Aviation Outlook: Widespread stratus with some vsby
restrictions is likely Monday night/Tuesday morning. Rain is
likely Thursday into Friday as a cold front pushes through the
region.

&&

.MARINE...
Tonight: A stationary front will meander along the coastal
waters. A minimal pressure gradient will cause winds to be very
light and variable tonight. Likewise, seas will be 2-3 ft. The
main concern is stratus building down to form sea fog this
evening and overnight. Given the aforementioned winds and an
inversion, areas of dense fog should be easy to form across the
waters, including the Charleston Harbor as well. Marine Dense
Fog Advisories may eventually be needed.

Tuesday through Saturday: A series of weak fronts will affect
the waters through mid-week, but no major impacts are expected.
A strong cold front will push into the waters Thursday night
into Friday. Northeast winds will prevail Friday night into
Saturday. There is a chance both winds and seas could reach
Small Craft Advisory levels Thursday night through Saturday, but
confidence remains fairly low at this time.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...
LONG TERM...
AVIATION...BSH
MARINE...


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