560
FXUS62 KCHS 132332
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
732 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/...
The early evening update shows an MCS passing into the Florida
Peninsula, with the northern extent of its convection starting
to diminish over the immediate area. As a result, we have shown
a steady diminishing trend to the rain early tonight. However,
with mid level impulses to continue to slide through, and
isentropic ascent to persist, we do maintain slight
chance/chance PoPs prior to midnight. Given that there is little
to no CAPE or elevated, we have removed mention of t-storms
early tonight. By late tonight the next MCS, impacting southeast
Texas and the lower Mississippi Valley will approach. That
occurs in tandem, with a warm front lifting north, and 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 /00Z TUESDAY THROUGH SATURDAY/...
An MCS to the south will pull away early tonight, with an
upstream MCS to approach late tonight, and pass nearby Tuesday
morning. A warm front will also lift north through the area
Tuesday morning.

It`s a rather complicated forecast, but it does look like flight
restrictions will occur for much of the upcoming 00Z TAF cycle,
with with at least some chance of SHRA at times overnight into
Tuesday. We can rule out a TSRA at KCHS and KJZI Tuesday morning
with the warm front. But probabilities are much too low at this
stage to mention in the TAFs.

We do show MVFR ceilings beginning the period at KSAV, and
taking until 10Z to develop at KCHS and KJZI. However, IFR is
possible at times, and adjustments could be made later on.

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

&&

.MARINE...
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 have a Small
Craft Advisory for both GA marine zones beginning this evening.
Also, on the SC waters as the back edge of the steadier rains
pull away and some drier air temporarily moves in, there can be
some gusts to near 25 kt. This includes the Charleston Harbor.
However, this looks to be infrequent enough that we don`t
require an advisory.

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...
SHORT TERM...BSH
LONG TERM...BSH
AVIATION...
MARINE...