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360
FXUS62 KCHS 230211
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1011 PM EDT Tue May 22 2018

.SYNOPSIS...
High pressure will remain to the east through Friday while a
trough of low pressure lingers to the west. Developing low
pressure over the Gulf of Mexico will slowly move north this
weekend through early next week, potentially maintaining wet
weather.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Deep moisture convergence will persist a little longer than
previously anticipated across some locations near and west of
US-301, with convection still ongoing due to upper difluence and
PVA near the local region. We now have slight chance/chance PoP
through about 1-2 am from about Millen to Metter and Reidsville,
but with little chance of activity elsewhere. The SREF
probabilities of low stratus after 09Z is now around 30-40%
inland from I-95, perhaps suggesting that it could be more than
just ground fog closer to daybreak. For now though we have
continued not mentioning fog in the forecast since condensation
pressure deficits are no lower than about 10-20 mb. temps are
about the same as 24 hours ago, so we have maintained
persistence regarding lows; upper 60s far inland, and lower to
mid 70s closer to the coast.

Previous discussion...
For most of the region the risk of convection has ended. The
exceptions will be near and west of US-301 across interior
Georgia, where boundary interactions will still allow for
scattered to locally numerous showers and a few t-storms through
mid to late evening. The overall thermodynamics are weak, but
with PWat around 160% of normal (1.90 inches) and a slow
steering motion toward the N-NE, locally heavy rains can still
occur near and west of a line from Reidsville to Portal and
Hilltonia. Latest guidance suggests that some of the oceanic
convection will make a run toward the upper Charleston County
coast, but we have held any mention of PoP off the land given
Forward Propagating Vectors that are offshore.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Atlantic high pressure will remain to the east while a weak
surface trough lingers inland. Aloft, the area will remain
between a ridge to the north and a trough to the south. Tropical
moisture will stick around for several more days, with PWATs in
excess of 1.75". Extensive cloud cover will limit surface based
instability during the period. We expect scattered to numerous
showers, especially during the afternoon hours away from the
coast which will be closer to the surface trough and thus better
convergence. Thunderstorms will be fairly isolated given the
limited instability, but high PWATs favor some locally heavy
rainfall.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Not much pattern change late this week into early next week with
high pressure remaining to the east and and low pressure to the
west. Will be watching for potential tropical cyclone development in
the south-central Gulf of Mexico. Models have been fairly agreeable
lately that the low will track toward the north-central Gulf Coast
region this weekend. This pattern will continue to maintain a
tropical air mass across southeast SC/GA and lead to higher than
normal rain chances. Temperatures should stay near to above
normal.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
Both KCHS and KSAV will be VFR through a large percentage of the
00Z cycle. However, there is some risk for low stratus and/or
ground fog at both sites between about 08Z and 13Z Wednesday,
and a chance for SHRA/TSRA in the afternoon. Any potential for
prolonged flight restrictions is too limited at this time to
show in the forecast.

Extended Aviation Outlook: A persistent tropical air mass will
lead to higher than normal rain chances through the weekend,
mainly each afternoon. Thunder chances will be relatively low
however. Some restrictions will also be possible from morning
low clouds and/or fog.

&&

.MARINE...
Tonight: No concerns as the region remains along the western
flank of Atlantic high pressure. Southerly winds 10-15 kt will
prevail with seas averaging 2-4 ft. Scattered showers and a few
t-storms will occur through the night, especially out near the
west wall of the Gulf Stream, with nothing more than isolated
convection in closer to shore.

Wednesday through Sunday: Broad Atlantic high pressure will
persist to the east through the weekend. Meanwhile, a weak
surface trough will exist inland through Friday, then surface
low pressure will move into the central Gulf coast region over
the weekend. Winds will remain onshore 15 kt or less through
Saturday afternoon, then potentially increasing to 15-20 kt
Saturday night and Sunday due to a tighter gradient. A modest
afternoon sea breeze will affect coastal areas each day.

&&

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

&&

$$
NEAR TERM...
SHORT TERM...JRL
LONG TERM...
AVIATION...
MARINE...