236
FXUS62 KCHS 261947
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
347 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/...
This afternoon through this evening: At the surface high
pressure is located to the east while to the west there are two
features of note. Hand analysis from 12Z this morning depicts a
shortwave trough on the lee side of the Appalachian Mountains
as well as a much weaker shortwave across MS/AL. The trough to
the lee of the mountains is the focus of possible precipitation
this afternoon, as the shortwave across MS/AL is quite weak and
likely will not be enough forcing to spur showers/thunderstorms.
Isolated showers and thunderstorms are possible this afternoon
across the SC Midlands, with some of those showers/tstorms
impacting far inland counties of the local CWA. However,
coverage is not expected to be great and PoPs have been lowered
from this morning`s forecast.

The thunderstorm risk this afternoon is very conditional, if
storms are able to form mesoanalysis suggests that DCAPE values
are upwards of 1200 J/kg, along with 40 knots of effective
shear. This would lead to a threat of damaging wind gusts. Low
level lapse rates are forecast to be around 7 to 7.5 C/km, which
would also lead to a marginal hail threat.

It will be another seasonably hot and humid day with highs
warming into the lower 90s with a few mid 90s possible in a few
areas. These temperatures combined with moderate levels of
humidity will support heat indices in the 98-101 range.

Overnight: Dry conditions will prevail into early Monday
morning. It will be warm/humid night with lows only dropping
into the lower 70s with mid 70s at the coast and beaches. The
record high minimums could be challenged, mainly at the
Charleston AFB/International Airport (KCHS) and Downtown
Charleston (KCXM), but current data suggest values will fall
just short of record levels.

&&

.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 /19Z SUNDAY THROUGH FRIDAY/...
Prevailing VFR through the 18Z TAF period at KCHS/KJZI/KSAV.
Showers and thunderstorms are possible this afternoon, however
the best chances remain inland from the terminals. KCHS/KJZI
have the best chance at seeing a shower/tstorm, however
confidence in direct impacts to the terminals remain low so
there is no mention in the 18Z TAFs.

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...
Rest of Today and 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...CPM
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...CPM/Haines
MARINE...CPM/Haines