455
FXUS62 KCHS 131956
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
356 PM EDT Mon May 13 2024

.SYNOPSIS...
A warm front will lift northward through the area Tuesday
morning, followed by a cold front from the west Tuesday night.
High pressure will return to the area by Thursday, followed by
another storm system this weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Convection will continue to move east along the Gulf Coast this
evening in association with a potent upper shortwave. However,
fairly widespread isentropic ascent north of the warm front is
spreading light to moderate rain across much of the forecast
area this afternoon. Slightly heavier precipitation could brush
past the southern half of our GA zones through early evening,
though most precip through late afternoon or early evening
should be relatively light. The brunt of the guidance shows the
ongoing precipitation tapering off by early to mid evening, then
a relative lull through much of the overnight.

Later tonight as the warm front lifts north, a weak surface wave
is expected to develop and move up the GA/SC coast. Models are
all over the place regarding coverage and timing of convection
associated with this wave. We focused the greatest PoPs over the
eastern half of the area late tonight, closest to the forecast
trajectory of the surface wave. Not a lot of instability is
expected, though models do hint at a pocket of 500-1000 J/kg
CAPE over coastal southeast GA late tonight where a few strong
thunderstorms are possible.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday and Tuesday night: The most active portion of the short
term period will come Tuesday and Tuesday night with a rather
complex forecast. As Tuesday morning begins, a warm front will
be lifting northward across the forecast area which should then
clear to the north by late morning. Forcing aloft will be
provided by a closed low and associated trough near the
Mississippi Valley that will gradually work eastward through the
day. At the start of the day, the main convective complex will
likely be crossing north Florida, with other convection ongoing
along and near the warm front. While the activity across north
Florida should stay south of the Altamaha, it could sneak into
far southern southeast Georgia along the coast and bring the
potential for strong to severe thunderstorms. Along the warm
front, thunderstorms should be ongoing and lifting to the north
and northeast through the morning. We have the highest rain
chances during this morning time period, with 60-80 percent
along the southeast South Carolina coast and along the Savannah
River and to the northeast. As the warm front gets north of the
Santee River and the activity to the south pushes out over the
coastal waters, we should see a lull before additional
convection tries to develop later in the afternoon after
recovery ahead of the cold front from the west. This activity
will likely extend well into the evening before the frontal zone
pushes off the coast late. Activity during this time should be
more scattered in coverage, and rain chances are held more into
the 30-40 percent range as a result.

Severe Thunderstorms: With the morning activity, the severe threat
will likely be tied to the environment along and near the warm
front. Model soundings do show MLCAPE around 1,000 J/kg, with 40-50
knots of mid-level flow. There is also some decent veering thanks to
the presence of the warm front that could yield SRH values on the
order of 150-200 m2/s2. So while damaging wind gusts are the primary
threat, the ambient wind profiles will also produce a low end
tornado threat. The threat should wane by midday as the activity
moves off to the northeast with the front. Attention then turns to
the afternoon and evening. While the veering noted in the morning
diminishes, mid-level flow remains notable in the 40-50 knot range.
Also, mid-levels dry out and yield DCAPE values of 1,000 J/kg or
more which should help to enhance the damaging wind gust threat.
This potential with scattered thunderstorms will continue into the
late evening hours.

Rainfall: Total rainfall amounts are still generally expected to be
in the 0.50-1.50" range. The highest amounts are expected along the
southeast South Carolina coast up through the Charleston Tri-County
region. Rainfall amounts, especially at the high end of the range,
will be very dependent on exactly where thunderstorms track.

Wednesday through Thursday: The area will be situated within the
circulation around an area of low pressure near the Outer Banks.
While a few showers could linger across the Tri-County region early
on Wednesday, the bulk of the day is expected to be dry. Weak high
pressure will build in on Thursday and bring a quiet weather day.
Highs each day are forecast to reach the upper 80s for most
areas.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
Shortwave ridging will pass through Thursday night ahead of a
shortwave that will cross into the Appalachians and the East Coast
through Saturday. A cold front is expected to approach Friday and
Friday night and push through the area on Saturday. An area of
thunderstorms is depicted by the model consensus and should impact
the area at some point during this time period. Active weather could
extend into Sunday as well, but there is uncertainty as to the
timing of the front and any thunderstorms associated with it. So the
overall theme of the long term period is increased rain chances and
above normal temperatures.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
A warm front will lift north late tonight and Tuesday morning.
This afternoon and tonight, moisture and forcing north of the
front will spread occasional light rain showers over the
terminals. Most guidance shows the brunt of the afternoon
precipitation shifting off the coast by mid-evening, then mainly
dry for much of the overnight hours. The statistical guidance
seems particularly aggressive with lowering ceilings this
evening. We are leaning more toward the SREF which is more
optimistic in keeping the MVFR/IFR ceilings across the SC
Midlands through much of the night.

At least MVFR ceilings seem fairly likely shortly after
daybreak Tuesday as the warm front lifts north through the area.
There should also be a better chance for robust convection
during the day Tuesday, with occasional vsby restrictions as
well.

Extended Aviation Outlook: Additional showers and thunderstorms
could impact the terminals with brief flight restrictions
Tuesday afternoon and evening. Otherwise, VFR conditions should
prevail.

&&

.MARINE...
Winds north of the warm front have been relatively weak today.
As the front lifts north this evening, winds over the GA waters
are expected to increase substantially, particularly over the
nearshore GA waters. We anticipate a period of 25 kt gusts late
this evening into the overnight, before the gradient relaxes a
bit. Over the outer GA waters, seas expected to rise to 6 ft
beyond 40 nm due to the strengthening SE flow. We issued a Small
Craft Advisory for both GA marine zones beginning this evening.

Tuesday through Saturday: A warm front will lift through the
waters early Tuesday and turn the flow from southeasterly to be
more southerly. Winds should mostly peak in the 15-20 knot
range, but there could be a few gusts to 25 knots at times.
Winds will diminish a bit later Tuesday, but then become
southwesterly and pick up ahead of a cold front that will push
offshore late Tuesday night. Winds should mostly be in the 15-20
knot range during this time. Winds will become more westerly
Wednesday night into Thursday, then southerly by Friday. Seas
will be highest Tuesday and Tuesday night, with 3-5 ft common,
and up to 6 ft expected in the outer Georgia waters and the
Charleston County waters. The advisory for the outer Georgia
waters goes through noon Tuesday and the Charleston County
waters goes into Tuesday evening.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 8 AM to 8 PM EDT Tuesday for AMZ350.
     Small Craft Advisory until 6 AM EDT Tuesday for AMZ354.
     Small Craft Advisory until noon EDT Tuesday for AMZ374.

&&

$$

NEAR TERM...JRL
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...BSH/JRL
MARINE...BSH/JRL