862
FXUS62 KCHS 191158
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
758 AM EDT Sun May 19 2024

.SYNOPSIS...
A cold front will cross through our area later today. High
pressure then prevails for most of this week, followed by
another storm system potentially impacting our area late this
week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early morning update: Difficult to tell...but surface boundary
(or outflow) appears to be draped across the forecast area from
Jenkins county to off the Charleston County coast into the
Atlantic. Short-wave circulation continues to fold its way down
through northern into central Georgia. Not much occurring
precip-wise at the moment (actually have a chunk of mainly clear
skies across the forecast area ahead of the circulation). But
that will change through the morning as shallow cooler air and
lower cloud cover begins to settle into the region from the
north while we heat things up further south. Guidance continues
to point at the development of showers/storms by early afternoon
along the leading edge of the wave in tandem with the surface
boundary. No significant changes to the forecast at this point.

Previous discussion...
Smaller scale convectively induced circulation continues to
advance northeastward off the Georgia coast early this morning.
Strong low level jet axis ahead of the wave extends up through
the coastal waters...evidenced by some unexpected gusty winds
from Savannah up through the Charleston coastal waters, while
also driving an axis of showers and thunderstorms across the
coastal waters. Convection will push away from the coast over
the next several hours.

Meanwhile, positive tilt mid level trough axis extends from the
mid Atlantic region down into the central Gulf, and attending
short-wave circulation pressing into northern Georgia. Surface
boundary extends across the far SE sliver of North Carolina and
back into the upstate South Carolina region along with some
convection that is slowly sagging into the central part of the
state.

Short-wave circulation and attending surface boundary will
advance down through the forecast area during the course of the
afternoon and off the coast tonight. Larger scale forcing for
ascent with the wave...in tandem with the boundary, daytime
heating and destabilization (1-2K J/Kg MLCAPE by early afternoon
south of the boundary) will kick off a compact area of showers
and thunderstorms that will track down through the forecast
area during the course of the afternoon. Given the high PWAT
values (1.5-2 inches) south of the boundary, heavy rainfall will
be a possibility and concern.

Biggest issue revolves around where convection develops and
the subsequent main area of impact. Recent CAM guidance
runs/trends press the surface boundary south of the Charleston
tri-county area quickly this morning and fire off convection
largely across the southern half of the forecast area. We have
made some southward adjustments to the highest pops/QPF amounts
with this forecast.

Tonight: Short-wave trough axis will slowly push off the coast
while surface high pressure wedges down from the north.
Convection will run its course this evening with thinning cloud
cover during the overnight hours. Cooler temperatures...dipping
down through the 60s for lows.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday: The mid-levels will consist of a positively tilted trough
just off the Southeast U.S. coast in the morning, and a ridge just
to our west. The ridge will slowly build into our area as time
progresses. At the surface, High pressure centered well to our north
will build down the coast as time progresses, with it`s southern
periphery making its way into our area. The High will bring dry
conditions with skies becoming mostly sunny/clear. Low-level
thickness values support temperatures in the middle 80s. But we went
a little below this due to the northeasterly surface winds and the
expectation that surface evaporation should limit temperatures.
Highs should peak in the lower 80s. Lows should range from the upper
50s far inland to the mid 60s closer to the coast.

Tuesday: A positively tilted mid-level trough will be just off the
Southeast U.S. coast in the morning, transitioning into a cut- off
Low in the evening and overnight. Meanwhile, a ridge will strengthen
over the Southeast U.S. Broad High pressure centered to our north in
the morning will shift off the Mid-Atlantic Coast as the day
progresses. Though, it`s southern periphery will continue to
dominate our weather during the day and into the night. Subsidence
will yield dry conditions with mostly sunny/clear skies. High
temperatures should be in the mid 80s, except cooler at the beaches.
Lows should range from the upper 50s far inland to the mid 60s
closer to the coast.

Wednesday: The mid-levels will consist of a cut-off Low meandering
off the Southeast coast, while a ridge prevails over the Southeast
U.S. At the surface, High pressure along the Southeast coast in the
morning will shift offshore into the afternoon. A front will slowly
approach from the north and northwest. Though, it won`t make it near
our area as the High will remain the dominant synoptic feature. Some
of the models hint at isolated weak showers trying to form along the
inland moving sea breeze late in the afternoon. But it`s still a
little too early to determine if the dry air in place will
completely squash these weak showers. Expect at least partly sunny
skies. Highs will peak in the mid to upper 80s, except cooler at the
beaches.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
Mid-level ridging will be over our region Wednesday night, followed
by west southwest flow on Thursday. A weak trough may pass to our
north Friday night into Saturday. Surface High pressure in the
western Atlantic on Thursday will shift further offshore as time
progresses. A cold front could approach from the north and northwest
later Friday, then lift north on Saturday. Expect mainly dry
conditions Thursday, with increasing diurnal convection Friday and
Saturday. High temperatures will be a few degrees above normal each
day.

&&

.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Largely VFR conditions will persist for the next few hours
although with an increased risk for MVFR cigs developing as we
get into the daytime heating cycle. With heating, the risk for
showers/tstms will increase by early afternoon with the best
focus for showers/tstms still looking to occur just south of
KCHS and impacting KJZI and especially KSAV. A TEMPO for TSRA
was included from 18-21z at KJZI to account for some coverage/timing
uncertainties. Prevailing TSRA remains for KSAV (20-00z).
Conditions were limited to MVFR for now with both cigs/vsbys
holding above alternate minimums. However, lower conditions may
eventually be needed as confidence in the timing, placement and
intensity of showers/tstms increases.

Convection diminishes this evening with some clearing taking
shape. Some low stratus is possible, particularly at KSAV where
the best coverage of rainfall is anticipated today.

Extended Aviation Outlook: VFR.

&&

.MARINE...
A brief period of gustier southerly winds will impact the
coastal waters early this morning. Surface boundary will move
down through the region as we go through the day and kick off
another round of showers and thunderstorms during the afternoon.
Winds veer northerly behind the front and will be increasing as
we go through tonight.

Monday: A cold front will be shifting offshore early in the
morning. Meanwhile, High pressure centered well to our north will
build down the coast and into our area as time progresses. The
strongest gradient will occur in the morning, with wind gusts just
short of 25 kt possible across much of the waters, and seas 3-5 ft.
The gradient will gradually weaken into the afternoon and overnight,
with seas gradually subsiding as well.

Tuesday and Beyond: NE winds on Tuesday will shift around to the SE
by later Wednesday as High pressure gradually shifts off our coast.
This will lead to a more typical summer wind pattern on Thursday
with the formation of the afternoon sea breeze.

&&

.TIDES/COASTAL FLOODING...
The combination of rising astronomical tides with the upcoming Full
Moon and moderate NE winds will cause tides to be elevated early
this week. Minor flooding is possible with the evening high tides
Monday and Tuesday, mainly along the South Carolina coast.

&&

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

&&

$$

NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...