716
FXUS62 KCHS 011811
AFDCHS

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

.SYNOPSIS...
A weak disturbance will move off the coast this morning. High
pressure will then prevail through Friday. A series of
disturbances will move through Saturday through Monday, then
high pressure will rebuild.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early afternoon update: Spotty showers have developed along the
sea breezes, largely across Charleston County. Convection is
struggling thus far, although some thunder is still a
possibility as instability builds further. No substantial
changes were made to the going forecast.

Previous discussion...
Morning satellite and upper air charts reveal a well defined
short-wave spinning off the North Carolina coast into the
Atlantic and slightly lower heights/cooler air aloft across the
coastal Carolinas into southeast Georgia. Early morning showers
along the southern periphery of the wave have weakened and moved
into the Atlantic. Morning fog/stratus is eroding/mixing out.

Rest of today: Upper level troughiness will weaken as upstream
ridging builds into the southeast coast through the afternoon,
although modestly cooler mid level air will linger into tonight.
With those cooler mid level temps, high resolution forecast
guidance and soundings show the development of 500-1000 J/Kg
MLCAPE this afternoon across the South Carolina counties...a bit
lower through southeast Georgia where mid level temps will be
warmer. Minimal larger scale forcing for ascent will exist across
the region this afternoon. But prevailing westerly low level
flow and development of the sea breeze will lead to respectable
convergence along the coast this afternoon with RAP13 guidance
suggesting the strongest convergence will be across the South
Carolina counties.

Upshot: Some pop-up showers and thunderstorms are a good bet
along the inland pressing sea breeze after 2 pm with the higher
probabilities looking to be across the South Carolina counties.
Severe storm risk is low, although SPC RAP data does show just a
touch (25-30 knots) of effective bulk shear across the SC
coastal areas...owing to modestly stronger mid level northwesterly
flow. This might support a stronger updraft or two.

Tonight: Ridging aloft builds overhead, while a weak pressure
pattern is found at the surface that shows Bermuda high pressure
offshore, another high near the Appalachians and a broad, but
weak trough in the local vicinity. The loss of heating will
quickly allow for convection along the sea breeze to come to an
end, and the rest of the night will be rainfree. The biggest
concern will be in regards to fog. Light to calm winds,
subsidence with a fairly strong inversion trapping moisture
underneath, and favorable condensation pressure deficits will
produce at least patchy coverage to the fog. However, some
guidance is hitting it harder, and shows not only greater
coverage, but also some potential for dense fog. There`s a
little cooler air that moves in as skies clear, allowing for
lows to get a few degrees cooler than it was this morning.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Deep layered ridging will prevail Thursday into Friday. Despite
a robust afternoon sea breeze both days and decent moisture
advection, strong mid-level subsidence should maintain dry
conditions. Above normal temperatures expected with highs in the
mid to upper 80s.

The upper ridge axis will shift just off the coast Saturday
morning, allowing upper shortwave energy to move into the area
from the west. Prevailing onshore flow should allow a sea breeze
to develop fairly early in the day and progress inland. The best
convergence and forcing for convection will exist inland.
Greater sky cover will knock a few degrees off high temps, with
low/mid 80s expected.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A quasi-zonal flow will exist Saturday night through Monday,
with a series of upper shortwaves moving through. Fairly deep
moisture will be in place, and a good sea breeze will develop
each day. Isolated to scattered showers and thunderstorms
expected during the period. Broad upper ridging Monday night
through Tuesday will bring mainly dry conditions with
temperatures climbing into the 90s in many areas.

&&

.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. Scattered showers and
thunderstorms Saturday through Sunday.

&&

.MARINE...
Today and tonight: The local waters will lie under or near the
western periphery of Bermuda high pressure, while a subtle
trough is found over nearby land areas. The resulting pressure
pattern is relaxed, and even with sea breeze circulations this
afternoon and evening, wind speeds will mainly be no higher than
10 or perhaps 15 kt. Seas will be just 2 or 3 feet. 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.

No marine concerns expected Thursday through Monday. Atlantic
high pressure will remain the dominant feature with a relatively
weak gradient in the area. Wind speeds will generally stay
below 10 kt except right along the coast with the afternoon sea
breeze, and seas will mostly run 2-3 ft.

&&

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

&&

$$

NEAR TERM...Adam
AVIATION...Adam