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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 202337
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
737 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/...
-- Changed Discussion --
Early evening analysis reveals the sea breeze from eastern
Berkeley County to near KNBC, then close to US-17 in Georgia.
Upstream and to the north a cold front is dropping south as it
crosses the border of North Carolina into South Carolina. That
feature has produced several severe weather reports, including
softball sized hail (4.5 inches) near Lumberton, NC. Extremely
rare indeed. Thew trajectories on that associated convection is
more east rather than south, but that will change as the front
sag further south. Additionally, convection near another
portion of the cold front is found across central and southern
Georgia, further enhanced by a weak short wave riding east.

The general "flavor" of the forecast remains unchanged, but we
did slow down the onset of the bulk of the convection from both
the north and the west by a couple of hours. We do have 20/30
PoPs early on due to the sea breeze and some activity attempting
to move in due to mesoscale boundary interactions. But the greater
chances occur after 9 or 10 pm, and not until after 11 pm or so
in Charleston area.

Given the amount of DCAPE (800-1000 J/kg) there does remain a
risk for isolated strong or maybe borderline severe wind gusts.

The record high minimum temperature for downtown Charleston is
71 degrees set in 2011. The low there so far today has been 71
degrees. If rain holds off long enough we could tie the record.

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.
-- End Changed Discussion --

&&

.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 /00Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
KCHS/KJZI/KSAV 21/00z TAF Discussion:

Tonight: Showers and thunderstorms associated with a cold front to
the north and west will attempt to congeal in the vicinity of
KCHS and KJZI, with the higher chances staying north and west
of KSAV. For now we prefer to show VCTS at all sites, but should
any direct impacts occur, then MVFR conditions would transpire.
The most likely timing for convection is between 04-08Z at KCHS
and KJZI. Should anything make it to KSAV, a similar time of
convection is warranted.

The front will drop south of KCHS and KJZI late tonight and
remain south of those terminals during Sunday, but it`ll take
longer at KSAV. North of the front IFR ceilings will occur, with
the steadier rains moving in during the afternoon. South of the
front at KSAV, the ceilings will be anywhere from IFR to VFR
Sunday morning, then higher confidence of IFR in the afternoon
with higher rain chances, as the front slides to the south.

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

&&

.MARINE...
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. In advance of the front SW winds will peak
at 15 or 20 kt, then 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...
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...
MARINE...