786
FXUS62 KCHS 080144
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
944 PM EDT Tue May 7 2024

.SYNOPSIS...
Atlantic high pressure will remain across the region through
mid week. A cold front will move through the area Friday
bringing cooler conditions heading into the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Short-wave ridging will continue to build into the southeast
region and overhead during the overnight hours. At the surface,
Atlantic high pressure prevails, with a subtle lee side trough
in place.

Overall, quiet conditions are anticipated tonight, with two
possible exceptions. The first is convection over and near the
southern Appalachians. Guidance is not handling this activity,
so we`ll definitely need to keep an eye on it, since the Corfidi
Vectors-Forward Propagation does have a steering flow into our
area. That said, increasing CINH, decreasing MLCAPE, and
subsidence should prevent it from getting here. So we maintain a
rainfree forecast.

Second will be the possibility of some low stratus/fog attempting
to advect in from the south-southwest closer to daybreak. All
available guidance keeps it south of the Altamaha River, so no
mention in the forecast.

Very mild temperatures, by early May standards through the
night. We`re some 5-10F degrees warmer than the same time last
night, so we`re only looking at lows in the upper 60s to lower
70s, even a little warmer near the coast. This is around 6-10F
degrees above climo, and within a degree or two of record high
minimums for May 8th.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/...
Wednesday and Wednesday night: The upper ridge axis will shift
offshore and the upper pattern will flatten out a bit. At the
surface, subtropical high pressure will continue to extend westward
into the forecast area and drive southwest flow for much of the day.
Skies should remain mostly clear, with just a muted cumulus field
expected, and model soundings are definitely not supportive of any
diurnal convection. Therefore, we have kept the forecast dry. The
main story will be temperatures. Low-level thickness values will be
supportive of widespread low 90s, with a few mid 90s possible for
interior southeast Georgia. Daily record highs are definitely
in play (see Climate section below). Fortunately, dew points
should mix out pretty well which will keep heat index values
solidly below triple digits. Overnight, expect dry and mild
conditions with lows only falling into the upper 60s and low
70s.

Thursday through Friday: Forecast difficulty and potential impact
will increase for the Thursday and Friday time period. Thursday is
expected to begin with a cold front situated well upstream, back
across the mid Mississippi Valley and into the Southern Plains. The
first part of the day should be similar to the last few days with
high pressure still the main feature across the forecast area
leading to southwest flow and warm conditions. Some degree of
convection should be ongoing across east TN, western NC, north GA,
and northern AL. The forecast for the afternoon and evening will
hinge greatly on the strength, position, and timing of this upstream
convection and its possible downstream propagation to the
Southeast coast. This time period is now starting fall within
the hi-res model run window, and model solutions range from a
strong (likely severe) squall line progressing across the
forecast area in the afternoon and evening hours to little to no
convection at all (favoring timing more into Thursday night and
Friday). With temperatures warming again into the low to
possibly mid 90s, there could be moderate destabilization in the
presence of strengthening mid-level flow ahead of any potential
convective line Thursday afternoon and evening. Lapse rates
steepen and nearly unidirectional 0-6 km shear on the order of
40-50 knots could set the stage for a large hail and damaging
wind threat. The area remains within SPC`s Day 3 Slight Risk
area and we will continue to highlight the severe potential
despite the uncertainties discussed. The cold front isn`t
expected to clear the area until later on Friday, and until it
does we could see rounds of convection Thursday night and again
early Friday. Given increased cloud cover and the effects of
convection, Friday temperatures are expected to be cooler. Look
for highs in the low to mid 80s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
The cold front will push well offshore Friday night, followed by
high pressure for Saturday. A weak boundary will pass by Saturday
night, with more high pressure for Sunday. A nice airmass change is
expected Saturday, with dry conditions and highs right around
normal. A modest warm up for Sunday will bring temperatures back
above normal by a few degrees. The forecast becomes more uncertain
early next week as model guidance suggests that southern stream
energy could move across the Deep South along a residual boundary.
Conditions could end up becoming quite unsettled, or the bulk of the
rainfall and convection could slide south of the area.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
KCHS/KJZI/KSAV: VFR will prevail through 00Z Thursday. All sites
will experience wind gusts around 15-20 kt Wednesday afternoon.

Extended Aviation Outlook: Primarily VFR. Chances of showers and
thunderstorms will increase late Thursday through Friday.

&&

.MARINE...
Tonight: Atlantic high pressure will continue across the local
waters, resulting in S and SW winds up to 10 or 15 kt and gusty.
Seas will average 2-3 feet early on, then build a foot
overnight.

Wednesday through Sunday: High pressure positioned to the east of
the local waters will maintain moderate south to southwest flow on
Wednesday. Winds and seas will then start to pick up later on
Thursday as a cold front approaches from the west. The front will
then shift offshore Friday and Friday night. Portions of the waters
could experience marginal Small Craft Advisory conditions ahead of,
and immediately behind, the passing front. Conditions will then
improve through the weekend with winds and seas both remaining well
below advisory thresholds. Another forecast issue for the local
waters will be the potential for strong thunderstorms Thursday
evening through Friday afternoon. The timing of thunderstorms
remains unclear for this time, but any storms that do develop and
move across the waters will be capable of producing strong wind
gusts.

&&

.TIDES/COASTAL FLOODING...
The upcoming New Moon (May 8) and recent Perigee (May 5) will lead
to elevated astronomical tides over the next few days.

Minor coastal flooding is possible along Charleston and coastal
Colleton Counties, including downtown Charleston, during the
evening high tides Wednesday and Thursday.

&&

.CLIMATE...
Record High Temperatures:
May 8:
KCHS: 93/1986
KSAV: 96/1986

May 9:
KCHS: 95/1963
KSAV: 95/1962

&&

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

&&

$$

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