Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 271109

Area Forecast Discussion
National Weather Service Charleston SC
709 AM 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,
followed by high pressure Friday into the weekend.


Today: No major changes with the latest forecast Moderate to
high confidence this period. Biggest forecast challenge is
determining the extent/timing of stratus/fog this morning.
Latest satellite imagery indicates widespread stratus retreating
mostly inland over the last few hours with a bit of fog well
inland where ceilings are lowest and farther east toward the
coast where clouds have mostly cleared allowing for better
radiational cooling. Could see inland stratus try to shift back
southeast a bit as low-level northerly winds increase a bit but
should see a quick improvement after sunrise, especially eastern
areas. Later today there should be a good amount of sun except
possibly close to the Altamaha River in GA where the low- level
flow will be more onshore. Could even see a few light
showers/sprinkles in this area as suggested by the high- res
model guidance but think the chances of measurable precipitation
are too low to mention. Highs should get well above normal,
near 80 northern/coastal areas to lower 80s elsewhere, warmest
in GA.

Tonight: Moderate to high confidence this period. High pressure
will prevail across most areas, especially in SC. Might see a
few light showers late close to the CSRA as deeper moisture and
upper forcing increase as tropical cyclone Zeta nears the
north-central Gulf Coast. Lows should mostly range from the
lower to mid 60s inland to lower 70s near the coast, still above
normal for this time of year.


Wednesday: The mid-levels will consist of high pressure located off
the Southeast coast in the morning and a strong trough/low over the
Southern Plains. The high will move further offshore with time while
the trough/low approaches. This will lead to southwest flow
overhead. At the surface, weak high pressure located to our
northeast in the morning will move further offshore and weaken with
time. Meanwhile, Hurricane Zeta will make landfall along the Lower
MS Valley in the evening. This storm will merge with a separate,
larger storm system in the same region. This newly merged storm will
shift to the northeast. Moisture associated with both of these
systems will continue to increase across our area with time as PWATs
exceed 1.5". Despite all of this moisture, the best lift and
rainfall potential should remain to our west, just outside of our
area. Though, some isolated light showers are possible, so we
generally have slight chance POPs west of I-95, during the afternoon
and into the night. QPF should be limited, if any. Temperatures will
be well above normal, especially at night.

Thursday: A strong mid-level trough and embedded low will be over
the Southern Plains in the morning. They will move eastward with
time, passing over our region late at night. A large storm system at
the surface is forecasted to overspread most of the eastern half of
the country. The bulk of the energy with this system is forecasted
to pass to our north during the afternoon and into the night.
However, a cold front associated with this system will approach our
area from the west during the day, then cross through our region
during the evening, moving offshore after midnight. Lots of moisture
originating from the Gulf of Mexico will be just ahead of the front.
Some models hint at a narrow band of 2.25" PWATs crossing through
our area in the evening, which is more typical of summer than late
October. However, the strongest lift will be to our north and this
is why there are indications the front will be in a weakening phase
as it moves through. The result will be much less rainfall than
PWATs would suggest. We only have chance POPs in the evening with
total rainfall ~0.1". Instability isn`t too great either, so we only
have a slight chance of thunder. The biggest concern may actually be
gusty winds ahead of, with, and just behind the front. If there`s
intense mixing, we could need a Lake Wind Advisory for Moultrie.
Beyond that, drier air and clearing conditions are expected to move
in from 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 broken.

Friday: A mid-level trough over the East Coast in the morning will
shift offshore with time. At the surface, a cold front will be
offshore in the morning and moving away. Meanwhile, strong high
pressure will become located to our north with time. Drier air and
subsidence associated with the periphery of this high will be
building into our area from the west. The result will be sunny
skies. Cold air advection within northwest to north surface winds
will lead to much colder temperatures. Highs will only be in the low
to mid 70s, which is actually near normal for this time of year.


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.


KCHS/KSAV: Moderate to high confidence for most of the 12Z/27
TAF period, with the lowest confidence regarding the extent of
stratus/fog late tonight. High pressure will prevail with no
rain expected through the period. However, abundant low-level
moisture will lead to the potential for some restrictions early
this morning and especially late tonight, possibly down to LIFR.
Looks like the best chance of low cigs will be at KSAV while
the best chance of low vsbys will be at KCHS where fog is more
likely due to a bit less cloud cover.

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


Today/Tonight: High pressure will prevail with no significant
concerns. However, there is a small risk that some fog could
impact areas near the coast, including Charleston Harbor, early
this morning and again late tonight.

Extended Marine: Weak high pressure will be located to our northeast
Wednesday morning and moving away from our area. Additionally,
Hurricane Zeta will make landfall along the Lower MS River Valley
Wednesday night, then combine with a separate storm system. This new
storm system will pass to our north on Thursday, with it`s trailing
front crossing through our area Thursday night. The surface pressure
gradient will steepen with these features. The result will be
rapidly increasing winds and building seas Thursday, so Small Craft
Advisories will be needed for all of the waters, including the
Charleston Harbor. The worst conditions are expected with frontal
passage Thursday evening. Gusts could exceed Gale force across
portions of the waters during that time period, along with steep,
wind-driven seas. The front quickly moves offshore on 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 steepen 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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