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000
FXUS62 KCHS 201947
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
347 PM EDT Sat Apr 20 2024

.SYNOPSIS...
An area of low pressure and associated front will pass through
the area and offshore tonight through Sunday. Dry high pressure
will return to the region early next week and prevail into the
middle of the week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Today: Current surface analysis revealed a retreat in the cold front
back north of the NC/ SC border this afternoon with CI imminent just
east of KCLT. Meanwhile, towards MS convection is ongoing and has
been heading east all day. Across coastal SC and GA, some weak
convection has tried to form along an inland moving sea breeze, but
updrafts have struggled so far. Visible satellite reveals a lot CU
trying to build only to be killed off by dry air entrainment in the
mid-levels. The latest ACARS sounding shows further evidence of this
with a pronounced dry slot around 500 MB (total PWAT ~ 1"). Either
way have kept slight chance PoPs in the forecast along the coast
as an isolated thunderstorm can`t be completely ruled out. Temperatures
have also rapidly risen today to around 90 degrees in most locations
as thermal profiles have completely mixed up to 850 MB.

This evening/ tonight: The convection currently near KCLT will be
heading east across the Piedmont of NC helping to further reinforce
the surface cold front (due to multiple cold pool deposits). As this
occurs, the front will again start to head south and cross the NC/
SC border. Simultaneously, convection that is currently in MS will
be over central GA. The cold front looks like it will sag south into
Berkley County late tonight with convection from central GA rapidly
spreading east along the stalled frontal zone. MLCAPE values are
forecast to be around 1500 - 1800 J/kg with SFC to 6 KM shear values
around 20 kts. Coverage along the stalled boundary appears that it
will be rather robust with most of the Tri-County likely observing
showers and thunderstorms sometime between 10 PM and 4 AM tonight.
The region is currently under a marginal risk from SPC and this
makes sense given the potential for isolated damaging wind gusts
(mid-level dry air). Precipitation chances south of I-16 on the
other hand, look much lower as southeastern GA will remain well
south of the incoming convection from the west and the cold front to
the north. Expect low temperatures in the upper 50s across SC, and
mid 60s across southeastern GA.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday and Sunday night: A tricky forecast as the cold front will be
situated directly across the forecast area from west-southwest to
east-northeast. The first part of the day should be in a relative
lull for showers and/or thunderstorms in the wake of departed early
Sunday morning convection. The front will slowly sag southward
across the area through the day and increased rain chances are
expected for the afternoon and especially into the evening as the
area gets into the cool side of the low and the front. While there
could be a few hours of sufficient instability for thunderstorms in
the morning just about anywhere, the risk area will steadily shrink
southward to primarily include the I-16 corridor and south including
Jasper and Beaufort counties. The greatest coverage of mostly
showers will track across the area from the late afternoon through
the late evening hours and that is when we have the highest rain
chances in place. Overall, the severe threat is low as the best
instability is progged to retreat southward before the arrival of
the better forcing. However, it`s not out of the question to see a
couple of stronger storms across our far south including McIntosh,
Long, Liberty, and Bryan counties in the late afternoon and early
evening hours. Daytime highs will be quite the forecast challenge
thanks to the presence of the front and anticipated north to south
gradient. Inland areas across Millen to Allendale and Moncks Corner
might only reach the mid 60s while locations around Savannah,
Hinesville, and Darien reach the low to mid 80s. Overnight should be
mostly dry with the low and front situated offshore. Lows are
forecast to cool into the upper 40s inland and the low 50s closer to
the coast.

Monday through Tuesday: Monday will bring a seasonally cool day as
the area is situated between the high to the west and the low center
and associated front offshore. This setup will drive cool northeast
flow across the area and some model guidance that there will be
enough residual moisture to produce some light rain showers Monday
morning and early afternoon. We have kept 20 percent rain chances
for much of the day, mostly along the coastal corridor. Cloud skies
in the morning should start clearing from the west in the afternoon.
Temperatures will be the main story, with highs only topping out in
the mid to upper 60s which would be on the order of 11-13 degrees
below normal for the date. Then for Tuesday, high pressure settles
in across the area and temperatures are expected to rebound nicely
back into the mid 70s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Overall, the long term forecast period looks to be quiet with
temperatures rebounding to be back above normal for most of the
period. High pressure will be the primary feature during the period,
though what looks like a dry front will drop through from the north
during the Wednesday night-Thursday period.

&&

.AVIATION /19Z SATURDAY THROUGH THURSDAY/...
20/18z TAF Discussion:

This afternoon: All terminals are VFR this afternoon with only
some CU in place. A surface cold front is slowly oozing south
across the NC/ SC border this afternoon, but will likely start
to pickup speed as showers and thunderstorms form upstream.
Later today, a sea breeze will start to move inland with only an
isolated storm possible along the coast.

Tonight: Showers and thunderstorms currently ongoing across TX/
LA will progress east and arrive at the terminals between 8 and
10 PM. As this occurs, the surface cold front will be located
just north of KCHS and KJZI. Generally, showers and
thunderstorms are expected to form and traverse east along the
frontal zone, which means KCHS and KJZI have the highest chance
of observing thunder overnight, while KSAV has a lower chance
(compared to the Charleston Terminals). Showers and
thunderstorms will then come to an end between 3 and 5 AM with
the surface cold front nudging south past KCHS and JZI, but
likely stalling right near or just north of KSAV. Behind the
cold front, cigs will rapidly fall into IFR conditions with
winds backing around from the north.

Sunday morning: A cornucopia of cigs is likely Sunday morning,
with IFR conditions likely at KCHS and KJZI, while conditions
could be bouncing around between IFR/ MVFR/ VFR at KSAV
(depending on the surface cold front position). Showers will
then return to the Midlands first Sunday morning only to pivot
and advect southeast towards the coast by late Sunday morning.

Extended Aviation Outlook: light restrictions will likely
linger across the area from Sunday evening through the first
part of Monday before improving. VFR thereafter.

&&

.MARINE...
Today: Southwest winds across the waters continue this afternoon
around 10 kts. A sea breeze has already started to move inland
this afternoon with the Charleston Harbor gusting to 15 kts, but
not much more than this is expected. An isolated shower or
thunderstorm could form along or near the sea breeze this
afternoon.

Tonight: A cold front will slowly sink to the south with
numerous showers and thunderstorms moving across the Charleston
Harbor and Charleston adjacent waters with a few of these storms
possibly producing wind gusts in excess of 35 kts. The cold
front will continue to sink south early Sunday morning and
likely stall near or just north of the Savannah River Entrance
by daybreak Sunday. Behind the cold front expect northeast winds
5 to 10 kts. Seas 2 to 3 ft.

Sunday through Thursday: Winds will start to surge out of the north
Sunday afternoon as a front clears through the waters. Northeast
flow will then strengthen Sunday night through most of Monday and
Small Craft Advisories will very likely be needed for all the local
waters. Conditions will then steadily improve through Tuesday with
no forecast concerns through the end of the forecast period.

&&

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

&&

$$

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