Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 100013

Area Forecast Discussion
National Weather Service Charleston SC
713 PM EST Sat Dec 9 2023

A strong cold front will cross the area Sunday evening,
followed by high pressure through late next week.


Early this evening: Overall, a quiet night is expected ahead of
an approaching cold front. The forecast area will remain in the
warm sector through the night, resulting in a very mild night.
In fact, lows are only expected to fall into the low 60s, which
is only a couple of degrees below typical high temperatures for
this time of year. There is good model consensus that land areas
will remain dry tonight, with the best chance for noctural
showers across the coastal waters and just off the Charleston
County coast. It is possible that a few showers could brush or
even move inland around McClellanville and Awendaw, but
otherwise most places will remain dry.


Sunday: The forecast philosophy has not changed significantly
from the previous forecast cycle. A sharp upper trough will dig
across the lower Mississippi Valley Sunday then become
negatively tilted as it pivots across the Southeast U.S. Sunday
evening, helping to drive a strong cold front through the local
area and into the coastal waters Sunday night. A corridor of
intense upper forcing ahead of the upper trough comprised of
strong DCVA, modest warm air advection and a well-defined window
of 250 hPa difluence will support several large areas of
widespread showers with isolated to scattered embedded tstms.
This activity is currently timed to reach far interior areas of
Southeast Georgia by late morning, then spread across the
remainder of Southeast South Carolina and Southeast Georgia
through the afternoon before most of the activity exits off the
coast during the mid-late evening hours. While the surface front
should clear the coast roughly in the 11/01-04z timeframe, the
anafrontal nature of the frontal surface suggests some degree of
shower activity will likely linger for several hours after
FROPA. However, expect a quick end to the rain and the onset of
rapid clearing during the early morning Monday as high pressure
and an expansive region of mid-level dry air begin to build into
the area from the west. Categorical pops near 100% look on
target for all areas into Sunday evening with rain chances
ending from west-east as the night progresses. Highs will warm
into the lower-mid 70s with temperatures with lows Monday
morning dropping into the lower-mid 30s over far interior
Southeast Georgia to the lower-mid 40s at the beaches.

The combination of widespread rain and extensive cloud cover
will tend to limit net instability across the area ahead of the
cold front. However, the lack of instability will likely be
overcome by the intense, deep-layered forcing noted on model
cross sections. This coupled with 0-6km bulk shear of 45-50 kt
and some MLCAPE as high as 500 J/kg could support an isolated
damaging wind event or two, or even an isolated, brief tornado
in a classic high shear/low CAPE environment. There are some
indications that pockets of higher instability could occur
across parts of the Charleston Tri-County where widespread rains
will arrive the latest. If this is realized, a slight uptick in
the severe weather potential could occur, but it does appear
that any meaningful higher risk for severe tstm development will
likely occur up to the north into northeast South Carolina and
eastern North Carolina.

Breezy to windy conditions will occur Sunday afternoon into
Sunday evening the the period of highest winds likely occurring
just prior to and after FROPA. Gusts 25-35 mph will be common
late afternoon into mid-evening with a potential for gusts as
high as 40 mph, especially along the lower South Carolina coast
when the low-level jet is at its most intense prior to FROPA.
Wind gusts could be higher over the elevated bridges across the
Charleston and Savannah Metro Areas as well as the exposed
bridges heading out to the various barrier islands. These winds
could pose a hazard to high- profile vehicles. A Lake Wind
Advisory will be needed for Lake Moultrie, although winds speeds
may be subdued somewhat in the warm sector by the poor mixing
profiles due to chilly water temperatures in the upper 50s. The
better potential for higher lake winds will hold off until cold
air advection kicks in after FROPA. A short-fuse Wind Advisory
may be needed as wind trends become more apparent, especially
for the lower South Carolina coastal counties.

Monday and Tuesday: Quiet and cooler weather will prevail as
high pressure dominates. Highs Monday will only warm into the
lower-mid 50s then warm into the mid-upper 50s for Tuesday. Lows
Tuesday morning will drop to around 30 for areas adjacent to
the CSRA and Southern Midlands to the mid 40s at the beaches.


Mainly quiet conditions will prevail through much of next week
with high pressure centered to the north. A subtle coastal
trough could develop off the coast by mid-week, but any
associated shower activity should remain offshore. Rain chances
could start to increase by Friday as a storm system begins to
organize over the Gulf of Mexico. Details of this system and how
it could impact Southeast South Carolina and Southeast Georgia
are highly uncertain this far out.


KCHS and KJZI: Through the overnight, the main concern will be
the potential for IFR ceilings to develop and impact the
terminals for short periods of time. Satellite imagery and the
KJZI observation actually showed that a small patch of IFR
ceilings developed just before 00z, but this has since moved
inland. Model guidance favors KCHS for the best chance of brief
IFR ceilings, so we have introduced a TEMPO group there.
Attention then turns to strengthening winds and increasing
shower and thunderstorm coverage on Sunday. Winds will pick up
by mid morning, and gusts will increase right on through the end
of the 00z TAF period. Frequent gusts up to and just over 25
knots can be expected in the afternoon and evening. The morning
should mostly be dry, with increasing showers in the afternoon
and then the potential for thunderstorms in the late afternoon
and early evening. Since thunderstorms are most likely near the
end of the TAF period, we did not explicitly include thunder,
but it is certainly something to keep an eye on.

KSAV: There continues to be a chance for low stratus
development in the early morning hours, but confidence isn`t
particularly high. For now, we have kept the forecast VFR but
amendments could be needed if IFR ceilings develop near the
terminal. Attention then turns to strengthening winds and
increasing shower and thunderstorm coverage on Sunday. Winds
will pick up by mid morning, and gusts will increase right on
through the end of the 00z TAF period. Frequent gusts up to 25
knots can be expected in the afternoon and evening. The morning
should mostly be dry, with increasing showers in the early
afternoon and then the potential for thunderstorms in the mid to
late afternoon. Since thunderstorms are most likely in the
latter part of the TAF period, we did not explicitly include
thunder, but it is certainly something to keep an eye on.

Extended Aviation Outlook: Widespread rain with vsby and cig
restrictions will occur through Sunday evening with conditions
improving early Monday. Gusty winds and possible low-level shear
are possible at all three terminals. Tstm probabilities are
still fairly low, although rumbles can not be ruled out. VFR
will prevail Monday through much of next week.


Tonight: Tonight, wind are expected to increase to 10-15 kts,
with gusts around 20 kts across portions of AMZ350 and 374 late
tonight/early Sunday morning. As dew points surge into the 60s
tonight and PWATs increase to around 1.4 inches scattered to
numerous showers and possibly a thunderstorm are expected over
the marine waters.

Sunday through Thursday: Southerly winds will begin to ramp up
Sunday ahead of an approaching cold front. Winds in the warm air
advection regime atop the chilly shelf waters will tend to
temper speeds a bit, but frequent gusts to 25 kt appear likely
over the South Santee-Edisto Beach nearshore and Georgia
offshore legs by afternoon. Similar conditions are expected in
Charleston Harbor where land heating influences will be greater.
A Small Craft Advisory has been posted for these areas.
Widespread will move across the marine area Sunday
afternoon/evening, ending from west- east early Monday. A few
heavier tstms could produce convective wind gusts in excess of
35 kt or even an isolated waterspout. A few Special Marine
Warnings may be need. Offshore winds will increase quickly after
the passage of the cold front with the risk for gales
increasing in the post-frontal cold air advection regime.
Frequent gusts to 35 kt appears likely for all legs out of the
Charleston Harbor from roughly Sunday evening through early
Monday. Gale Watches have been posted for all legs to account
for this, excluding Charleston Harbor (although it may be
close). Gale Warnings will likely be issued with the early
Sunday morning update. Seas will peak 4-7 ft nearshore waters
with 5-9 ft over the Georgia offshore leg and the outer portion
of the South Santee-Edisto Beach nearshore waters. The next
chance for Small Craft Advisory conditions could come as early
as Wednesday as both winds and seas build in response to a
tightening pressure gradient with the development of a coastal
trough offshore.


KCLX remains operational, but level 2 data is not being
distributed to external users due to an internal hardware
failure. We are still awaiting the arrival of new parts to
resolve this problem. Until then, level 2 data will not be
available. Radar data is available for all connected AWIPS
users. Level 3 data is also available for some external users.


MARINE...Small Craft Advisory from noon Sunday to 6 AM EST Monday for
     Small Craft Advisory from noon to 6 PM EST Sunday for AMZ350-
     Gale Watch from Sunday evening through late Sunday night for
     Gale Watch from Sunday evening through late Sunday night for



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