Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 141520

Area Forecast Discussion
National Weather Service Charleston SC
1020 AM EST Thu Dec 14 2017

High pressure will persist across the region today. A dry cold
front will push through Friday night before high pressure
returns Saturday and Sunday. Another cold front will arrive
Monday into Tuesday before shifting offshore on Wednesday. High
pressure should then persist into late week.


As of 1015 AM: A few patches of thin cirrus clouds will continue
to pass mainly over SE GA today. I will update the forecast to
adjust the sky forecast a little higher.

Previous Discussion:
Satellite shows cirrus will likely linger across Southeast
Georgia a bit longer than originally expected. Adjusted sky
grids to show increased cloud cover through the morning hours.
The rest of the forecast is on track.

Secondary push of cold air advection will push off the coast
prior to daybreak as shortwave energy passes by to the north.
This will quickly give way to weak warm air advection later
this morning as a weak clipper emerges off the Mid-Atlantic
coast and its trailing cold front stalls out across the Northern
Midlands into the Pee Dee. While some thin cirrus will brush
far southern areas this morning, the main cloud axis will
translate south yielding full insolation across Southeast South
Carolina and Southeast Georgia. Rising H8 temperatures and
corresponding low-level thicknesses will support highs in the
lower-mid 60s for many areas this afternoon with locations
across portions of Long, McIntosh and Liberty Counties away from
the coast potentially topping out in the upper 60s.


Tonight: The boundary layer will decouple quickly after sunset
as a weak stationary front lurks north of the Santee River. The
front looks to remain north of the area overnight. Clear skies
and light/calm winds during the evening hours will promote fast
temperature falls as radiational cooling is maximized, but
cirrus will steadily thicken after midnight enhanced by a 170 kt
stretching from east Texas into the Virginia Tidewater. This
will slow down thermal falls during the early morning hours
Friday. However, still expect lows to drop into the upper 30s
inland with lower-mid 40s at the coast. A few mid 30s will be
possible in some of the normally colder areas of northern
Dorchester and Berkeley Counties away from the Santee Cooper
Lakes, including the Francis Marion National Forest.

Friday: A mid/upper lvl low positioned over the Great Lakes and
Northeast will help push a weak cold front through the region early
this weekend. Latest guidance indicates the front will remain dry,
but mid/upper lvl-moisture along with strong divergence associated
with the right-rear quadrant of an upper lvl-jet should produce
widespread cloud cover over the Southeast. Given the setup, temps
should remain a bit cooler inland where high clouds and fropa occur
first. In general, temps will peak in the upper 50s inland to
low/mid 60s near the coast. Dry and cold high pressure will push
into the area Friday night, resulting in a gradual decrease of cloud
cover late. Lows should dip into the lower 30s inland where
radiational cooling is strongest and to the mid/upper 30s closer to
the coast.

Saturday and Sunday: Conditions will remain quiet this weekend and
early next week as dry high pressure becomes centered over the
Southeast on Saturday, then slowly shifts offshore on Sunday. Temps
will be slow to warm on Saturday despite a full day of sun and west
downsloping wind. In general, afternoon highs should peak in the
mid/upper 50s for most areas. A few locations could reach 60 along
coastal Georgia. Strong radiational cooling under clear skies will
support Saturday night lows in the mid/upper 30s away from the
coast. A light southerly flow will then develop over the Southeast
as the center of the high shifts offshore. This should lead to
noticeably warmer temps Sunday afternoon before the onset of
increasing moisture and clouds late. In general, Sunday highs should
peak in the mid 60s for most areas. A few areas could approach the
upper 60s near the Altamaha River in Southeast Georgia.


Cloud cover should expand over the Southeast Sunday night with
increasing moisture and isentropic ascent occurring well ahead of a
cold front approaching the area. Chances of showers should arrive
late Sunday night and increase in coverage through Monday as a plume
of moisture characterized by PWATs near 1.75-2.0 inches advects over
the Southeast along/ahead of the slowly approaching front. Temps
could peak into the upper 60s to around 70 degrees on Monday despite
clouds and increasing shower coverage, mainly due to the strength
and position of the mid/upper lvl ridge of high pressure to the
southeast. Temps will remain mild Monday night and Tuesday while mid-
lvl energy continues to traverse the Southeast before the main mid-
lvl trough axis and associated cold front shift over the area late
Tuesday into early Wednesday. For this reason, at least chances of
showers will be possible Monday night into early Wednesday before
dry high pressure returns behind the cold front shifting offshore.



Extended Aviation Outlook: VFR conditions will prevail at both CHS
and SAV terminals through Sunday. Increasing chances of flight
restrictions will be possible Sunday night into Monday with the
arrival of showers and cold front.


Today: Winds and seas will diminish this morning with the
passage of a shortwave to the north. Expect west to southwest
winds to settle into the 10-15 kt range this afternoon with seas
subsiding to 1-3 ft.

Tonight: West winds will persist through the night ahead of a
weak stationary front lurking north of the Santee River. Speeds
will remain 10 kt or less with seas 1-2 ft.

Friday through Monday: Dry high pressure will prevail until a weak
cold front approaches from the west and passes offshore Friday
evening into Friday night. Cold air advection behind the front will
promote a fair amount of mixing into a 40 kt low-lvl jet and could
result in marginal Small Craft Advisory level winds over northern
South Carolina waters and offshore Georgia waters Friday night into
early Saturday. However, latest guidance indicates winds/seas should
fall just short of Small Craft Advisory level criteria. Conditions
will likely improve over the weekend as dry high pressure becomes
centered over the area Saturday, then slowly shifts offshore on
Sunday. A slight uptick in conditions is then expected on Monday as
a cold front approaches the area. In general, west winds will become
south and remain at or below 10 kt Saturday and Sunday, then
increase from the south/southwest to 10-15 kt on Monday. Seas will
be no higher than 1-2 ft Saturday and Sunday, but should build to 2-
3 ft on Monday.




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