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079
FXUS62 KCHS 121919
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
319 PM EDT Sun May 12 2024

.SYNOPSIS...
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High pressure will exit the coast early Monday with a storm
system approaching from the west. An active weather pattern will
start on Monday with multiple rounds of showers and
thunderstorms possible through Wednesday.
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&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Today: An impressive shortwave has now moved off of the coast
of New England this afternoon with ageostrophic convergence
focused across TN/ NC/ and SC. At the surface, a ridge axis
extends through these states with surface high pressure closed
off near the FL/ GA border. The jet streak overhead is slightly
fractured, with a subtropical jet from OK/ MS/ AL to GA putting
SC in a LFQ. This has allowed a rather thick cirrus shield in
areas to manifest, but temperatures have only been held down by
a degree or two at most. Late this afternoon, a sea breeze will
begin to push inland with winds turning from the southeast. No
precipitation is forecast.

Tonight: A sea breeze will move inland about a tier of counties or
so, before stalling and washing out. Meanwhile, surface high
pressure that was over the GA/ FL state line will weaken and start
to washout just off of the SC coast early Monday morning. The
collapse of the surface high will be due to (1) a departing jet
streak and (2) waves of PVA moving overhead. This consistent
reinforcement of positive vorticity atop mid-level ridging will
allow atmospheric moisture to recover rather quickly across SC with
winds backing around from the southeast. No precipitation is
expected tonight, but skies will likely be mostly cloudy to
overcast with cloud bases lowering. Expect low temperatures
mostly around 60 degrees inland with temperatures near 70
degrees at the beaches.
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&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
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Mid level low initially over the Central Plains Monday morning
will shift eastward to the Mississippi Valley through Tuesday,
with a series of shortwaves expected to track over the local
region ahead of this feature. A surface low takes a similar
path, with a warm front lifting north into the region. Moisture
returns back to the area with PWats surging to over 1.75 inches,
which is well above seasonal climatology. This sets the stage
for a period of unsettled weather.

Monday will start dry then rain chances should increase from the
southwest through the day and into the evening. Consensus indicates
that instability during this time period will remain rather limited,
so while thunder will certainly be in play, the severe threat is
low. The highest shower/thunderstorm coverage and rain chances will
be during the latter half of Monday night and Tuesday when the
better forcing arrives. Still uncertainty in the convective
evolution and specific timing, but wind shear values will be
supportive of storm organization. Instability is in question
depending on how earlier convection works out, but current model
progs feature the highest CAPE values over southeast Georgia.
Regardless, all areas will need to be watched for stronger to severe
storms. Marginal Risk for severe weather from SPC Day 3 Outlook
persists. Area-wide rainfall totals throughout the event currently
average in the 2-3 inch range, with isolated higher amounts
possible. Pockets of heavier rainfall could result in ponding on
roadways and minor flooding especially in urban and poor drainage
areas.

The bulk of activity should transition offshore through Tuesday
night with decreasing rain chances in its wake.

The main upper wave and associated surface reflection will pass
across the mid-Atlantic states on Wednesday and eventually offshore.
With some upper support and lingering moisture, isolated to perhaps
scattered showers/thunderstorms will be possible. Outside of
convection, winds will become gusty with gusts to around 20-25 mph.
Temperatures should peak in the mid to upper 80s.
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&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
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Ridging briefly passes across the region on Thursday with no weather
concerns. More unsettled weather is expected to return late week
into the weekend as the next low pressure system tracks towards the
East Coast. Forecast details still need to be worked out, but
regardless, at least scattered showers and thunderstorms will be
possible both Friday and Saturday. Temperatures through the period
are forecast to be near to above normal.
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&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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KCHS/ KJZI: VFR conditions currently across the Charleston
terminals this afternoon with a thick cirrus shield currently
overhead. Surface high pressure has continued to nudge east this
afternoon and is centered over the GA/ FL state line. Winds
should start to back this afternoon as the high pressure
centers south of the Charleston terminals, but this will be
relatively short lived though as a sea breeze is forecast to
cross both Charleston Terminals between 00 and 02z. No
precipitation is forecast today or tonight. Showers with a
slight chance of thunderstorms will then approach the Charleston
Terminals Monday. For the current TAF package, have started
lowering the CIGS for Monday morning.

KSAV: VFR currently at Savannah with surface high pressure
centered to the south near the GA/ FL state line. A weak sea
breeze will try to push inland across GA, but will likely get
hung up near the coast. Overnight, mostly calm winds and no
precipitation is forecast. For the current TAF package, have
started lowering the CIGS for Monday morning.

Extended Aviation Outlook: Flight restrictions are possible in low
clouds and showers/thunderstorms Monday afternoon into midweek as a
storm system impacts the region.
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&&

.MARINE...
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Today and Tonight: Surface high pressure is currently located
near the GA/ FL state line and will move offshore this evening.
West winds will gradually turn from the southwest and then south
late tonight. A weak sea breeze will form this afternoon with
with in the Charleston Harbor gusting 10 to 15 kt. Overnight,
winds will be 5 to 10 kt with seas 1 - 2 ft.

Monday through Friday: No concerns over the marine area on Monday.
Winds will increase Monday night into Tuesday and will remain fairly
gusty into Wednesday as low pressure tracks towards the East coast.
Seas also build and while it looks fairly marginal at this time,
there is potential for a period of Small Craft Advisories over
portions of the waters, especially the outer Georgia and Charleston
county waters. Conditions improve for Thursday. Next weather system
is expected late week into the weekend with conditions currently
held below advisory criteria.
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&&

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

&&

$$

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