278
FXUS62 KCHS 020216
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1016 PM EDT Wed May 1 2024

.SYNOPSIS...
Atlantic high pressure will extend west across the Southeast
U.S. into next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Late this evening: The main forecast challenge overnight will
concern fog and stratus potential. Model guidance is trending
pretty aggressive with fog development and coverage, beginning
just after midnight and quickly spreading across most of the
forecast area. This make sense given good low-level moisture,
light to calm winds, and broad subsidence aloft. Given that we
saw at least some dense fog last night across the interior, it
seems plausible similar type fog can be expected tonight since
we have not any real airmass change. The main difference will be
location. Guidance favors fog development first across the
Charleston Tri- County, which should then spread across nearly
all of southeast South Carolina and into portions of southeast
Georgia along the Savannah River. We also feel like the dense
fog potential is high enough to warrant introduction into the
Hazardous Weather Outlook. Lows are forecast to be near 60 away
from the immediate coast and the mid 60s along the coastal
corridor.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Thursday and Friday: Strong subtropical ridging aloft will
dominate the Southeast U.S. both days with the area located
along the western flanks of Atlantic surface high pressure
centered well offshore. While low-level moisture will remain
somewhat seasonable with dewpoints in the 50s and 60s, broad
subsidence aloft and the resulting lack of any meaningful mixed-
layered instability will support a mainly dry forecast through
the period. A rouge shower can not be completely ruled out
Friday afternoon ahead of the sea breeze as the upper ridge
shifts offshore and mid-level capping weakens a bit, but chances
for anything measurable will likely remain below the
mentionable threshold of 20%. A few showers/tstms could drift
into into the far inland areas from the west Friday evening as
weak shortwave energy passes by to the north and west. Forecast
soundings at KRBW, KJYL and KMHP show a steadily weakening mid-
level cap during this time as the upper ridge shifts farther out
into the Atlantic. Slight chance pops around 20% were
maintained across the interior to account for this. Highs will
warm into the mid-upper 80s each afternoon away from the beaches
with overnight lows dropping into the mid 60s well inland to
near 70 at the beaches.

Saturday: The risk for scattered showers/tstms will increase on
Saturday as a weak mid-level weakness settles across the
Southeast States. Forcing for ascent will remain fairly weak and
ill-defined in the vicinity of the weakness per model omega
vertical cross-sections, but weak to moderate instability
coupled with low-level convergence near a fairly progressive sea
breeze circulation and potential convective outflow
interactions would support a slightly more active day compared
to the previous few where subtropical ridging dominated aloft.
20-60% pops were maintained Saturday with the highest gridded
pops clustered well inland ahead of the sea breeze. Highs will
warm into the lower-mid 80s.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
The pattern will be more reminiscent of summer next week. The
weak mid-level weakness over the Southeast U.S. will quickly
begin to fill and push offshore Saturday night into Sunday with
broad, subtropical ridging dominating aloft thereafter. The
region will remain along the western periphery of Atlantic
surface high pressure centered well offshore. This pattern will
support a more typical, diurnal convective pattern with activity
generally concentrating along/ahead of the afternoon seas
breeze with the best rain chances concentrating in the Saturday
and Sunday periods with the weakness aloft. Weak shortwave
energy is progged to pass by to the north on Monday, but most of
the forcing with this feature looks to remain over the Pee Dee
into central/eastern North Carolina. Temperatures will slowly
rise through the period, peaking in the upper 80s to lower 90s
by Tuesday.

&&

.AVIATION /02Z THURSDAY THROUGH MONDAY/...
For the 00z TAF period, fog and stratus is the primary forecast
challenge. The setup and model guidance suggests that IFR
conditions are likely at the TAF sites, and that dense fog will
be possible as well.

KCHS and KJZI: Fog and stratus development is expected to begin
in the early morning hours and we have started IFR conditions by
around 06-07z. We have then included a TEMPO group from 08-12z
to account for dense fog, though it could linger past 12z for a
little bit. A return to VFR should occur by around 13-14z.
Currently we are not expecting any shower or thunderstorm
development in the afternoon.

KSAV: Current thinking is that fog will develop to the northeast
of the terminal and then gradually spread in in the pre-dawn
hours. The lowering of the flight category is expected to happen
later than at KCHS and KJZI, and we have timed in MVFR
conditions by 09z. Confidence is potentially dense fog is lower,
so for now we have kept the 10-12z TEMPO group with just IFR
conditions. VFR should return by around 13z and prevail
thereafter with no current concerns for shower or thunderstorm
development in the afternoon.

Extended Aviation Outlook: Flight restrictions possible in
overnight/early morning fog and stratus. Isolated to scattered
showers and thunderstorms are possible Saturday through Monday.

&&

.MARINE...
Tonight: Surface high pressure and relaxed pressure gradient
will remain in control across the coastal waters resulting in
overall lighter winds. Sea breeze push later this afternoon will
keep onshore winds slightly elevated until early evening with
speeds of 10 to 15 knots. Winds 10 knots or less anticipated
tonight. Late tonight there will be the formation of some fog
over land areas, some of which could move into the Charleston
Harbor and the Atlantic waters very close to shore.

Thursday through Sunday: There are no major concerns through
the period. A broad southerly flow will prevail through the
weekend with the local waters located along the western
periphery of Atlantic high pressure centered well offshore.
Typical sea breeze wind enhancements are expected each afternoon
along the land/sea interface and Charleston Harbor. Seas will
generally remain 3 ft or less through the period.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...
LONG TERM...
AVIATION...BSH
MARINE...Adam