Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 280228

Area Forecast Discussion
National Weather Service Charleston SC
1028 PM EDT Tue Oct 27 2020

High pressure will linger through the middle of the week. A
storm system will bring impacts to the region Thursday which
will help push a cold front across the region Thursday night.
High pressure then returns for the weekend.


Late this evening: No changes with this update.

Early this evening: Surface analysis shows a weak front still
situated to the south, with higher thetaE air pooled across
south and southwest Georgia. Satellite imagery shows mid clouds
steadily spreading in from the southwest as the upper
anticyclone over the southwest Atlantic starts to get deflected.
Overnight, the aforementioned front is expected to lift
northward, but any real forcing for ascent should be displaced
well to the west where the best thetaE advection is progged to
be. We have maintained a dry forecast. Overall, no significant
changes to the forecast through sunrise.


Wednesday: Aloft, ridging persists over the area while a deep
low resides over the Southern Plains. At the surface, the region
is sandwiched between high pressure offshore to the northeast
and Hurricane Zeta to the southwest. Zeta is expected to make
landfall along the LS/MS coast where it will then track
northeast. Its mid/upper-level counterpart looks to merge with
the stronger upper- level low, which will cause Zeta to undergo
an extra-tropical transition. Surface winds shift primarily to
the southwest in the afternoon advecting offshore moisture;
however, most of the deeper, substantial moisture associated
with the remnants of Zeta is expected remain to our west.
Isolated showers are possible in the far inland SC/GA counties,
with PoPs capped at slight chance/low-end chance in those areas.
Max and min temps are forecast above-normal for this time of
year; low to mid 80s during the day with overnight temps in the
upper 60s and lower 70s across the area.

By Thursday, the low pressure system will be situated just to
our west and shall continue to track to our northeast throughout
the day. The strong upper-level system tilting to the west with
height will provide an abundance of DPVA/forcing, but its
target area maintains just west of the forecast area. Again,
isolated showers are possible in the far inland SC/GA counties
during the day. By Thursday night, a cold front trailing the
system will approach the region. Models are struggling to
analyze the amount of rainfall that will be accompanied by the
front. While surface forcing and a decent amount of moisture
trailing along the eastern seaboard (PWATS ranging from 1.5" to
2.5" across model guidance) are present, substantial upper level
forcing and instability are lacking. A slight chance of thunder
is possible with any isolated showers that form over the
forecast area just prior to the arrival of the front. QPF is
minimal at this point, yet some models show the possibility for
a half-inch of rain. On the other hand, the bigger concern is
for gusty winds ahead of, with, and just behind the front. If
there is intense mixing, we could need a Lake Wind Advisory for
Moultrie. Beyond that, drier air and clearing conditions are
expected to move in from the west after midnight. This will be
the last day of 80 degree temperatures for our area this week,
which could put some record high temperatures at risk of being

Friday: A mid-level trough over the East Coast in the morning
will shift offshore with time. Meanwhile the cold front will
have moved offshore by the morning. High pressure will build to
the north and a significantly drier air mass will move in.
Additionally, subsidence will result in clear skies. Cold air
advection within northwest to north surface winds will lead to
much colder temperatures. Highs will return to near-normal; only
reaching the low to mid 70s.


Zonal flow is expected to prevail in the mid-levels Saturday,
followed by a long-wave trough over the East Coast Sunday into
Monday. At the surface, high pressure passing to our north
should bring dry conditions and below normal temperatures.


Overall, VFR conditions are expected to prevail at KCHS and KSAV
through 00z Thursday. We will have to watch for possible fog and
stratus late tonight, with the best chances being around KCHS.
The TAF`s still feature shallow ground fog at both sites
starting around 10z. Current thinking is that any flight
restrictions in fog and stratus will remain inland of KCHS.

Extended Aviation Outlook: A storm system will bring flight
restrictions Thursday and Thursday night. Additionally, gusty
winds are expected Thursday into Friday.


Tonight: The center of broad high pressure will shift over the
western Atlantic late tonight. Steady ENE winds should continue
across the marine zones overnight, speeds between 5-10 kts. Seas
are forecast to range between 2-3 ft tonight.

Extended Marine: Weak high pressure located to our northeast
Wednesday morning will eventually shift into the Central
Atlantic. Additionally, Hurricane Zeta is expected to make
landfall along the Lower MS Valley Wednesday night, then combine
with a separate storm system. This new storm system will pass
to our north on Thursday, with its trailing front moving
offshore late Thursday night. The pressure gradient will rapidly
increase Thursday and will result in increasing winds and
building seas. Small Craft Advisories will likely be needed for
all of the waters, including the Charleston Harbor, with gusts
increasing to 25 kt and seas building to 4-6 ft across the
majority of the marine zones. The worst conditions are expected
during the frontal passage Thursday evening. Gusts could reach
Gale force across portions of the waters during that time
period, along with steep, wind-driven seas building up to 7-8 ft
in portions of the waters. The front is expected to move
offshore by Friday and high pressure builds in from the west,
which will lead to a brief window of lower winds and seas in the
afternoon hours. However, conditions should deteriorate again
Friday night as cold air advection and the pressure gradient
steepens again. These near gale conditions should persist
through the weekend.


Record warmth possible Thursday, October 29:

KCHS: 85/1946 and 72/1984

KCXM: 82/1984 and 72/1984

KSAV: 87/1996 and 71/2019





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