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000
FXUS62 KCHS 220226
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1026 PM EDT Sun Apr 21 2024

.SYNOPSIS...
An area of low pressure and associated front will push through
the area and offshore today. High pressure will then return to
the region and prevail through much of the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
The cold front certainly is an impressive feature, and is across
northern Florida and continuing its trek southward. Temperatures
have dropped considerably behind the front, and down into the
50s everywhere. Compare that to yesterday at a similar time and
we`re some 20-25F colder.

All rains have ended, although there might be a few sprinkles
far inland late as an upper trough moves in. Otherwise, with
some cyclonic flow still hanging on through the night due to a
subtle post-frontal trough the main challenge will be how much
clearing can we achieve. Most guidance implies that we`ll stay
mostly cloudy or overcast, but recent satellite trends have been
showing at least partial clearing far inland. We will adjust as
necessary.

A steady feed of northerly flow will drop temperatures to at
least 50-55F, with potentially some colder readings in the 40s
across parts of our northwest tier. If we do get enough
clearing, it might even be a bit colder, and could allow for
patchy fog to form where winds go light due to the wet grounds.

Closer to daybreak and due to the formation of a wave of low
pressure well offshore on the baroclinic zone, some showers over
the ocean could approach Charleston County. However, this is too
low of a probability to mention in the forecast.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Expect a quiet and dry pattern during this period. The upper trough,
centered over the Mid Atlantic states on Monday, will move eastward,
with the southern extent of the trough axis east of the region by
late Monday/Monday night. Deep layer ridging is expected to build in
from the west Monday night through Tuesday night. By Wednesday, the
upper flow becomes more zonal as an upper trough passes well north
of the area over NE U.S./New England area, which is expected to push
the low level/surface ridge eastward into the Atlantic. Models are
showing a weak surface boundary/front to sag southward into at least
the northern part of the forecast area by late Wednesday. However,
models differ on amount of deep layer moisture associated with this
front. The GFS seems more robust than the other models. For now,
continued a blended model solution for the PoPs, which keep the area
dry. However, will need to monitor this time frame for the potential
for increased rain chances.

Temperatures expected to be below normal Monday through Tuesday,
then back to normal to slightly above by Wednesday. Highs generally
in the upper 60s Monday and lower 70s by Tuesday. Monday night lows
expected to be quite chilly for this time of year, in the lower to
mid 40s inland, and upper 40s to lower 50s closer to the coast.
Tuesday night lows in the upper 40s to lower 50s inland, and mid to
upper 50s closer to the coast.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Overview: Models continue to show that the bulk of this period will
remain dry with temperatures near to slightly above normal through
at least Friday, then possibly 4-6 degrees above normal by Saturday
and Sunday.

A broad upper trough looks to hang on over the eastern U.S. with an
associated weak surface front possibly sitting over the region
Wednesday night through Thursday. This front/boundary then sags just
south of the area Thursday night and Friday, then seems to wash
out/weaken Friday and beyond. Again, current forecast keeps PoPs
below 10% through this period. However, we will monitor the
potential for higher PoPs Wednesday night through Thursday night as
a broad upper level trough, weak surface boundary and increased deep
layer moisture sit over the region. Low amplitude, deep layer
ridging tries to build from the west Friday through Saturday, and
may even increase in strength by Sunday. As the ridging builds later
in the period, the low level flow veers to southeast, which will not
only help to warm temperatures, but gradually increase low level
RH/dewpoint temperatures. Despite increasing low level RH, current
guidance keeps surface dewpoints in the upper 50s to lower 60s,
highest coast, by weekend, which is not too bad.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
22/00Z TAF Discussion:
KCHS/KJZI/KSAV: All sites will remain with MVFR ceilings through
the night, with considerable moisture trapped beneath the
inversion, and still some cyclonic flow in place. However, some
clearing is trying to work its way east, and there could be
periods of VFR as well. A greater chance of prevailing VFR
though is expected Monday morning and thereafter, as moisture
finally decreases with high pressure building from the west-
northwest. Northerly winds will average about 10-15 kt and a bit
gusty at times through the entire forecast cycle.

Extended Aviation Outlook: VFR will prevail through mid/late
week.

&&

.MARINE...
Tonight: Recent trends, some cold advection, and eventually
decent isallobaric pressure climbs has prompted us to go with
Small Craft Advisories on all Atlantic waters. N winds will
average 15-20 kt, with frequent gusts of 25 kt or greater. Seas
will build to 3-5 feet, and highest on the Charleston County
waters and the Georgia waters beyond 20 nm. Winds in Charleston
harbor will average near 15 kt through the night, so no advisory
for that marine zone.

Monday through Friday: Cold advection and tightening pressure
gradient behind a cold front is expected to produce low end SCA
conditions for AMZ350 and AMZ374. Have raised an SCA for AMZ350
for later tonight through Monday, and continued SCA for AMZ374
for a longer period, through early Tuesday afternoon. The SCA
for AMZ374 hangs on longer for seas of 5 to 7 feet slowly
subsiding. Northeast winds of 15 to 20 knots with gusts of 25 to
28 knots possible for AMZ350 and AMZ374 through Monday. Could
even see a short period of gusts to around 25 knots for
AMZ352/354, especially Monday morning into early afternoon.

Expect northeast winds to gradually decrease by later Monday,
fall below SCA levels all waters Monday night, generally 15
knots or less. Seas of 4 to 7 feet, highest AMZ350/374 on
Monday, will subside to 3 to 5 feet Monday night and beyond,
except holding on around 6 feet AMZ374 through early Tuesday
afternoon.

No highlights expected by later Tuesday through Friday. A weak
cold front may sag over the waters Wednesday night through
thursday night, which could surge northeast winds back to 15 to
20 knots, but not expected to reach SCA levels. This front is
shown by all models to push just south of the waters later
Thursday night through Saturday, with northeast winds of 15
knots or less and seas 3 to 5 feet.

Rip Currents: Gusty northeast winds and building seas will lead to
an elevated risk of rip currents on Monday. Have continued a
Moderate risk all beaches for Monday. Decreasing winds and seas on
Tuesday should lead to lower risk for rips.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 8 PM EDT Monday for AMZ350.
     Small Craft Advisory until 5 PM EDT Monday for AMZ352-354.
     Small Craft Advisory until 2 PM EDT Tuesday for AMZ374.

&&

$$

NEAR TERM...
SHORT TERM...RFM
LONG TERM...RFM
AVIATION...
MARINE...