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000
FXUS62 KCHS 212224
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
624 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 finally
through the entire forecast zones. Temperatures have dropped
considerably behind the front, and down into the 50s over most
communities. Compare that to yesterday as we`re some 20-30F
colder than a similar time last evening.

Widespread rains roughly near and east of I-95 will steadily
taper off as the rain shield moves offshore, and all places will
be rainfree by 9 or 10 pm, if not sooner. Some cyclonic flow
still hangs on through the night with a subtle post-frontal
trough. Thus it`ll remain mostly cloudy to overcast through the
night.

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.

&&

.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 /22Z SUNDAY THROUGH FRIDAY/...
21/18z TAF Discussion:
KCHS/KJZI: Both terminals were VFR early this morning, but are
now both impacted by restrictions. At KCHS, the cold front has
since oozed south with borderline IFR/ MVFR cigs in place. This
will likely hold in place through the evening hours. At KJZI,
the cold front has stayed just north of the terminal, but since
then showers and thunderstorms have formed and moved across the
terminal restricting the cigs and vsbys. A few more rounds of
showers and thunderstorms are forecast for the Charleston
terminals through 22z. By 00z, showers and thunderstorms will
come to an end as the surface cold front clears the area. A
return of the IFR/ MVFR cigs is then forecast on the backside of
the cold front. After midnight, cigs will slowly start to
recover.

KSAV: Showers are currently pushing across KSAV with a surface
cold front approaching from the west. Prevailing MVFR cigs
will then settle in as convection pushes offshore and a cold
front moves through. The risk for IFR cigs looks to hold north
of the terminal. VFR will return overnight as high pressure
builds in.

Extended Aviation Outlook: Could see a short period of MVFR
CIGS into mid/late Monday morning, especially KJZI and KCHS,
then expect VFR to return all sites later Monday morning through
mid/late week.

&&

.MARINE...
Tonight: North winds increasing in speed to 15 to 20 kt with
gusts approaching 25 kt, especially late tonight. It looks like
Small Craft criteria will be reached Monday morning as the
surface low deepens off of the NC coast tightening the pressure
gradient. As such, Small Craft Advisories are in effect for the
offshore GA waters and nearshore SC water adjacent to Charleston
County starting 6 AM Monday.

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 from 6 AM to 8 PM EDT Monday for AMZ350.
     Small Craft Advisory from 6 AM Monday to 2 PM EDT Tuesday for
     AMZ374.

&&

$$

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