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000
FXUS62 KCHS 180831
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
431 AM EDT Thu Oct 18 2018

.SYNOPSIS...
Cooler high pressure will build over the region today and
Friday before shifting offshore Saturday. A stronger cold front
will advance through the area Saturday night, followed by cool
high pressure through the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Pre-dawn: The cold front was pushing toward the GA/FL border
early this morning with gradually increasing northeast flow and
falling surface dew points lagging just a bit behind this
morning but on schedule to push south through the area prior
to daybreak. Cloud coverage is somewhat tricky as elongated areas
of mid and high clouds extend over the southeast states but not
much in the way of stratocu to this point.

Today: High pressure is forecast to build east from the Ohio
Valley to the Mid Atlantic region and expand south over GA and
the Carolinas. Forecast soundings across our region indicate
moisture at stratocu level is expected to pool across southern
GA under a well defined inversion between 3-5 kft. Across our
SC zones, it looks a bit drier in that layer but soundings
suggest more in the way of mid level moisture and higher
expectations of altocu hanging around. Given the complexity of
the potential sky coverage today, partly sunny skies were an
average call at this point. It should remain dry with only small
chances for isolated showers along the immediate coastal areas
closer to the Altamaha River where slightly deeper moisture is
expected to linger into the day. The break from the very warm
temps has arrived with temps in the 70s today, coolest northern
zones where highs may struggle to top the lower 70s. Across
southeast GA, temps should reach the mid 70s with some upper 70s
far southern zones (especially if we lesser coverage of
stratocu). Breezy conditions on the beaches and barrier islands
where northeast flow remains steady in the 20-25 mph range
between tight thermal and moisture gradients from north to south
and between land and the Gulf Stream.

Tonight: We should see a decent low level gradient across much
of the forecast area between high pressure over NC and a weak
coastal trough off of northeast FL. Dry weather and cooler temps
are on tap for the most part. Lows will have dramatic gradients
over the area, ranging from the upper 40s northwest tier to the
upper 60s on southern barrier locations such as Sapelo Island
GA.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Dry high pressure is expected to prevail over most areas Friday into
early Saturday morning. A more developed coastal trough was noted in
the synoptic 18/00Z model suite by late Friday night. Model
prognoses vary, with the NAM and Canadian most aggressively
resolving the trough, and the GFS and ECMWF a little slower with
development and overall weaker. Nonetheless, this feature could
be responsible for isolated shower development primarily over
southernmost coastal waters, though some brushes with nearby
coastal zones cannot be entirely ruled out. By Saturday, the
next cold front is likely located near the Appalachian mountains
and rapidly progressing towards the forecast area. Compression
in advance of the front will drive maximum temperatures higher.
Of note, the latest GFS fails to show overly impressive
soundings for precipitation potential, and peak POPs Saturday
have been lowered slightly. The front will then clear the
forecast area by late Saturday night, and further declining POPs
and temperatures ensue. Behind the front, a rain-free Sunday
will feature below-normal temperatures.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
Mostly dry conditions and moderating temperatures are expected
heading into early next week as surface high pressure builds in
behind the cold front. The GFS and ECMWF indicate development of a
coastal trough as high pressure pushes offshore Monday night into
Tuesday, and slight chance POPs remain for southeasternmost zones.
Forecast uncertainty increases after Tuesday with possible pressure
falls near the south-central plains.

&&

.AVIATION /07Z THURSDAY THROUGH MONDAY/...
VFR. Northeast winds will increase toward daybreak with breezy
conditions into midday.

Extended Aviation Outlook: VFR conditions are expected to prevail at
both terminals. Brief flight restrictions will be possible due to
reduced ceilings and/or vsbys under showers as a cold front
approaches and crosses the region Saturday into Saturday night.

&&

.MARINE...
A significant northeast surge was building down our coast pre-dawn
and this trend will continue through the daytime hours, reaching
southern GA waters before mid morning. Small craft Advisories
are in effect all waters except the CHS Harbor where near-SCA
are certainly possible later this morning. Winds will increase
to 20-25 kt across most waters and tend to weaken this evening
over northern SC waters while model trends keep a strong low
level gradient and steady NE flow to the south of the Savannah
River well into tonight. Seas will build to 4-6 ft near shore
and 5-7 ft well offshore and slowly decrease below SCA levels
over CHS waters later tonight.

Ongoing Small Craft Advisories will gradually drop off as elevated
winds and seas continue to subside through later Friday. Winds will
turn onshore later Friday as surface high pressure shifts further
offshore, and continue veering SW into Saturday as the next cold
front rapidly advances towards the region. With cold front passage
expected late Saturday night into pre-sunrise Sunday morning, winds
will veer generally north. Rapidly building high pressure will lead
to another surge in winds/seas, and Small Craft Advisories may be
needed by early Sunday morning. Winds then veer more northeasterly
as conditions gradually subside through the day Sunday into Sunday
night, with NE flow generally persisting through early next
week.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 11 PM EDT this evening for AMZ350-
     352.
     Small Craft Advisory until midnight EDT Friday night for
     AMZ374.
     Small Craft Advisory until 6 AM EDT Friday for AMZ354.

&&

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