058
FXUS62 KCHS 180552
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
152 AM EDT Sat May 18 2024

.SYNOPSIS...
A storm system will bring impacts to our area this weekend.
High pressure returns to our region next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Earlier round of convection has moved out of the far southeast
Georgia counties at this juncture with precip free conditions
and mild temperatures out there. Upstream, short-wave trough
axis stretches from Arkansas into central Texas and will be
advancing into the lower Mississippi River Valley by morning.
Channel of strengthening low-mid level flow/moist advection
ahead of the trough (along with short-wave forcing) is looking
to develop from the Louisiana Gulf Coast up through western and
southern Georgia through the overnight hours. Already seeing an
increase in convection along the LA coast and into parts of
MS/LA in response, and recent high-res guidance runs suggest
convection will further increase into central/southern Georgia
by early morning, although details vary from run to run as
typically the case. We will need to keep an eye on development
upstream as we may be looking at a round of stronger storms
rolling through the region during the morning...particularly the
Georgia counties.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/...
Much of this period is expected to be the most active for the entire
forecast period through the next work week. Models show an upper
level trough over the lower MS River Valley early Saturday, moving
eastward toward the forecast area through Sunday. Conditions look
the most favorable for showers/thunderstorms later Saturday
afternoon through Sunday. Peak values of CAPE and bulk shear will be
later Saturday afternoon and Saturday evening, which is the main
time frame that the SPC has our entire region in a SLT Risk for
severe storms. Have kept high likely/low end categorical PoPs for
much of the area on Saturday and Saturday evening, chance Saturday
night, and then likely again Sunday. The threat for any severe
storms looks too low to mention for Sunday due to a significant
decrease in CAPE, despite the passage of a surface cold front and
the presence of the upper level trough. By later Sunday night and
Monday, the upper trough axis will move offshore, allowing a cold
front to push south of the area. High pressure builds in from
the northwest Sunday night and Monday, which will bring slightly
cooler and drier conditions.

Temperatures above normal Saturday, near normal Sunday and possibly
a tad below normal behind the cold front on Monday.

Heavy Rainfall Potential: Blended models solutions continue to point
toward later Saturday afternoon and evening for the most likely
window for locally heavy rainfall. The area with the highest chance
for heavy rainfall appears to be our coastal counties, especially
from the Charleston Tri-county region, southward to the Savannah
River. However, there continues to be uncertainty in the exact
placement of the heavy rainfall, since localized boundaries produced
by convection/thunderstorms will likely dictate where the heaviest
rainfall occurs. Thunderstorm induced boundaries could collide with
a weak seabreeze close to the coast Saturday afternoon, which is why
we are leaning toward higher chances for the heaviest rainfall to be
over our coastal counties.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
This period looks to be much quieter, with little/no chances for any
significant rainfall and temperatures above normal. Another cold
front may impact the area later Thursday and Friday with at least
slight chances for showers/thunderstorms. However, the timing of
this front and whether or not there will be sufficient deep layer
moisture to support precipitation remains uncertain. Temperatures
expected to be above normal during this period, especially by
Thursday and Friday as a deep layer ridge builds to the south-
southwest of the area, keeping our region under low level west-
southwest flow.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
KCHS/KJZI/SAV: Precip has largely exited the region for the moment.
There may be some isolated/scattered showers that move through
the KCHS/KJZI terminals through early morning although overall
chances are too low to include in the forecast. We are
maintaining overall VFR conditions overnight, although some
lower stratus development and reduced vsbys remain a
possibility.

On Saturday: Increasing favorable chances for showers and some
thunderstorms to roll through the region Saturday morning and
into the afternoon hours, with the greater impact likely to
occur at the KSAV terminal. We have a period of flight
restrictions at all three terminals between roughly 14Z and 20Z
with further timing refinements highly likely. Bulk of
showers/thunder will exit the region Saturday evening.

Extended Aviation Outlook: Saturday night through Sunday:
Periods of showers and thunderstorms are expected with brief
flight restrictions possible, especially later Saturday
afternoon and evening. Isolated to scattered strong to severe
storms will be possible Saturday afternoon and evening.

Sunday night through Wednesday: VFR expected to prevail.

&&

.MARINE...
The surface pattern will support S o SSW winds between 10 to 15
kts, with wave heights forecast to gradually build to 2-3 ft by
late tonight.

No highlights are expected through the period. The waters will
remain under the influence of a ridge of high pressure well to the
southeast and lower pressure well inland, to the northwest. This
will keep southwest winds of 15 knots or less and seas generally 2
to 4 feet through Sunday. A cold front is expected to push through
the waters during the day on Sunday. Behind this front, winds will
veer to north-northwest and increase to 15 to 20 knots. Seas
building to 3 to 5 feet.  The increased winds/seas are not expected
to persist long. They should begin to subside a bit by later Monday
as winds become more northeast at 15 knots or less, with seas 2 to 4
feet Monday night through Wednesday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...Adam
SHORT TERM...RFM
LONG TERM...RFM
AVIATION...Adam