648
FXUS62 KCHS 011918
AFDCHS

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

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

&&

.NEAR TERM /THROUGH TONIGHT/...
Mid level trough axis has progressed into the Atlantic with the
back edge of the trough and cooler mid level air progressing
eastward out of the coastal Carolinas. Latest SPC mesoanalysis
shows a narrow corridor of 500-1000 J/Kg MLCAPE along the coast.
Enough low level convergence/instability to pop some convection
along the SC coast as well as along a subtle line of convergence
from CHS back up to around Lake Marion in inland SC. No lightning
thus far, although there are a few enhanced updrafts with cloud
ice (per satellite imagery) and some rumbles of thunder yet
occur.

Rest of the afternoon: Isolated to scattered showers and
potentially some thunder will be the rule until early evening
with the best coverage anticipated across southeast South
Carolina, and especially the tri-county area. Severe threat
remains low, but a brief heavy downpour is possible.

Tonight: Short-wave ridging will build into the southeast
through tonight with weak surface high pressure remaining draped
across the region. Convection will wane/end quickly this evening
with quiet weather thereafter. Biggest concern remains fog
possibilities. With light/calm winds...increased surface
dewpoints and larger scale subsidence, patchy to areas of fog is
a good bet, particularly down through southeast Georgia and
perhaps the tri-county area where we are getting a little
rainfall late this afternoon. A Dense Fog Advisory may
eventually be needed later later overnight/early Thursday
morning.

&&

.SHORT TERM /THURSDAY 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 TUESDAY/...
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 /18Z WEDNESDAY THROUGH MONDAY/...
KCHS/KJZI/KSAV: Showers and possibly a thunderstorm or two are
possible this afternoon, primarily at KJZI and KCHS with a
lesser chance at KSAV. Given the lower probs for thunder, I have
removed the mention from the terminal forecasts with the 18Z
forecast and will amened as necessary.

VFR conditions heading into this evening. Development of fog
appears likely at all terminals later tonight into Thursday
morning. We have introduced IFR visibilities at the terminals
with the 18Z forecasts, but there is a risk for LIFR toward
Thursday morning. Conditions return to VFR Thursday morning
after 13Z.

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...Adam
AVIATION...Adam
MARINE...Adam