181
FXUS62 KCHS 262320
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
720 PM EDT Sun May 26 2024

.SYNOPSIS...
Hot conditions are expected through Memorial Day. A cold front
will move into the region Monday night and stall into mid week.
High pressure will return for the second half of the week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Late this evening: Satellite imagery tells the story with the
weak cumulus field from the afternoon quickly evaporating with
the loss of diurnal heating. There certainly are some strong
storms across the South Carolina Upstate and western North
Carolina, but that are on a trajectory that will keep them well
north of the area through the late evening. Therefore, the
forecast is dry through the overnight and there are no
significant fog concerns. It should be quite mild overnight,
with lows only dipping into the low to mid 70s.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
Monday: A broad trough axis will exist across the central
United States Monday morning with a parade of embedded
shortwaves ejecting northeast. The embedded waves will advect
across the Mid-Atlantic states Monday afternoon with the core of
the DCVA remaining well north of the region. As this occurs,
the wave axis will begin to take on a negative tilt with SC and
GA just on the cusp of a split jet streak (RRQ and LFQ). Ahead
of this parade of shortwaves and accompanying PVA, weak pressure
falls will occur on the lee side of the Appalachians. Several
runs of the NAMnest have been fairly consistent on showing an
approaching MCS in the morning hours of Monday quickly falling
apart only to have fresh convective initiation to occur across
the Midlands of SC and the Piedmont of NC. Bulk shear values at
this time are around 30 kt with net storm motion to the east 30
to 40 kt. Hodographs are rather straight which would support
initially discrete cells with some upscale growth possible into
clusters as multiple cold pool amalgamations occur. The main
uncertainty for Monday is for how long will these updrafts be
able to maintain themselves. NAM and GFS forecast soundings
still show impressive capping Monday afternoon across coastal GA
and SC. In fact, Monday morning and early afternoon looks dry.
Highs will likely reach into the lower 90s as 850 MB temperature
surge towards 19 C. Both the NAM and GFS then quickly erode the
CAP by the evening hours (less so towards Long and McIntosh
counties). For the inland SC counties, enough modification to
the thermodynamic profiles appears likely with storms advecting
east from the Midlands. Storms will have the potential to
produce damaging wind gusts and even large hail. As the storms
move across the area, they will likely start to weaken. Expect
low temperature Sunday in the upper 60s to lower 70s.

Tuesday: A double-barreled shortwave will dive south out
Ontario/ Quebec with positive amplification taking place. This
will drive a surface cold front to the coast where it will come
to an abrupt halt. The true 850 MB cooling will be held back
though as winds veer around from the northwest and downslope
flow commences. This type of setup usually produces some of the
warmer days across the area (especially at the coast) where a
sea breeze gets pinned at the beaches. Given this, have blended
in the the NBM 75th percentile for high temperatures on Tuesday
with widespread lower 90s forecast. The only chance of
precipitation will be along the coastal strip in proximity to
the surface cold front. Low temperatures Tuesday night will be
mostly in the mid 60s (inland) to lower 70s at the beaches.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Global ensembles continue to advertise a seasonably strong
amplified wave (1 to 2 SD anomaly) over Quebec and New England
on Wednesday which moves offshore next weekend. The latest run
of the deterministic GFS is now again advertising wave breaking
occurring next weekend, but not nearly as impressive as the
25.12z model run. Taking a look at the WPC Cluster Analysis for
this time period shows the rapid wave breaking remaining in the
minority of solutions. Only one cluster shows wave breaking
occurring on Saturday which accounts for only about ~25% of all
GFS, ECMWF, and CMC ensemble solutions. On Sunday, there is more
broad ensemble support for wave breaking to occur southeast of
the Canadian Maritimes. This working with an overall slower
progression of the wave would favor slightly below normal
temperatures starting Thursday and continuing into Saturday. A
warming trend will then commence starting Sunday (as well as a
return of afternoon showers and thunderstorms).

Wednesday: The primary wave axis will be located near Ontario
and Quebec Wednesday with a secondary shortwave on the southern
flank of the primary wave axis. During the day Wednesday, the
surface cold front will likely be located near the SC/ GA coast
with the 850 MB front lagging behind. Temperatures will still be
warm on Wednesday with highs in the lower 90s. No precipitation
is expected.

Thursday and Friday: By Thursday, the surface cold front will
be offshore with surface high pressure nudging in from the Ohio
River Valley. Surface high pressure will slowly head southeast
through the day with the potential for the cold front to buckle
across our southern zones as southern stream energy ejects east
out of Texas. The confidence and predictability of this is
extremely low at this point, but given the time of year this is
certainly possible. For now, have kept the forecast mostly dry
for Thursday and Friday, but future forecast packages will need
to keep an eye on this to see if PoPs need to be introduced.

Saturday and Sunday: The mid-level wave will be amplifying off
of the Canadian Maritimes with surface high pressure exiting the
Mid- Atlantic coastline. Warmer and more humid conditions will
return by Sunday.

&&

.AVIATION /23Z SUNDAY THROUGH FRIDAY/...
VFR conditions are expected to prevail at KCHS, KJZI, and KSAV
through 00z Tuesday. Thunderstorms become a concern at all 3 TAF
sites in the last couple hours of the TAF period and we could
need to introduce some impacts and flight restrictions with
subsequent TAF issuances.

Extended Aviation Outlook:

Monday: VFR expected in the morning hours ahead of an
approaching mid-level wave. Late in the afternoon, showers and
thunderstorms across the Midlands of SC will advect southeast
and approach the terminals by the evening hours. If these storms
hold together all the way to the GA/ SC coast is still very
uncertain at this point given a stout 700/ 850 MB cap in place.
If the storms do hold together, restrictions is visibilities and
ceilings are possible with gusty winds.

Tuesday: A surface cold front will be pinned along the SC/ GA
coast. Winds will be out of the northwest around 10 kt. There is
a slight chance of showers and thunderstorms at the terminals
due to their proximity to surface cold front. VFR conditions are
expected, except with any showers and thunderstorms that
directly impact the terminal.

Wednesday through Friday: VFR as a surface cold front remains
south of the region. There could be some precipitation late
Thursday/ early Friday which might produce some restrictions in
visibilities and ceilings. Otherwise, VFR.

&&

.MARINE...
Tonight: Southerly winds this afternoon around 10 knots will
prevail, with 10 to 15 knots and some gusts to around 20 knots
in the Charleston Harbor and the coastline as the sea breeze
circulation sets up. Conditions along the coastline will
diminish this evening, and southerly winds around 10 kt will
persist through the night.

Monday through Friday: Marine conditions remain below Small
Craft Advisory levels through the week. South to southwest will
largely persist through midweek until a cold front pushes east
of the waters on Wednesday. High pressure will be the dominant
feature for late week. Winds will average 15 knots or less and
seas 2-3 feet, with occasional 4 feet early in the week.

&&

.CLIMATE...
Record High Minimum Temperatures:

May 27:
KCHS: 76/1991
KCXM: 79/2019
KSAV: 77/1878

&&

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

&&

$$

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