Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 090627
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
127 AM EST Fri Dec 9 2016

.SYNOPSIS...
Colder high pressure will extend over the area through the first
half of the weekend. A weak trough of low pressure is expected
to develop over the Atlantic coastal waters Saturday night and
Sunday. By next week, a series of cold fronts are expected, with
the first one arriving by Monday night, then potentially a
stronger cold front by mid week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Tonight: A deep mid/upper level cyclone moving through eastern
Canada and its associated shortwave will track through the
northeast quadrant of the country. At the surface, the leading
edge of the arctic air is overspreading much of the nation east
of the Rockies, including the local forecast district.

Expect variable amounts of high clouds associated with a strong
upper jet passing over the area tonight. However, a gradual clearing
from west to east is anticipated late, supporting cooler lows
late while strong cold air advection persists across the region.
In general, temps will dip into the mid/upper 30s away from the
coast.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/...
Overview...This period will be marked by much colder temperatures
and little or no chance of precipitation.

Friday...The area will be just in the wake of a strong cold front
with polar high pressure building from the Northwest. Even with
mostly sunny skies, strong cold advection will hold high
temperatures to around 50 north to the lower 50s south. Winds will
not be more than 5-10 mph, thus the wind chill effect will be
minimal. Friday night...Expect some of the coldest temperatures so
far this season as high pressure continues to settle over the area.
The pressure gradient weakens allowing winds to drop to calm/near
calm under mostly clear skies. Expect temperatures to reach a solid
freeze in most areas away from the immediate coast. Still going for
mid 20s well inland upper 20s to lower 30s elsewhere.

Saturday...High pressure moves to just north of the region with
light northeast winds. Given models not showing much warm advection,
expect highs will struggle to reach back into the lower to mid 50s.
Saturday night...Not quite as cold as Friday night, but still
freezing temperatures likely from I-95 west and mid to upper 30s
closer to the coast. The one factor that could keep temperatures
from getting this cold, especially closer to the coast, will be the
potential for a developing coastal trough of low pressure over the
near shore waters as low and mid level flow veers to east-southeast.
Some models actually trying to produce some light QPF, but have kept
slight chance pops for the coastal waters, possibly reaching extreme
coastal areas of South Carolina counties toward day break.

Sunday...Although models differ on the strength and position of the
developing coastal trough, they seem to agree that it will weaken
and move northward through the day. Surface high continues moving
northeast into the Atlantic ahead of a developing storm system over
the central U.S. by late in the day. Have kept slight chance/low end
chance pops mainly over the water with again slight chance scrapping
the immediate SC coast, mainly Charleston county. The presence of
the coastal trough offshore most of the day and a departing high to
the north will hold a weak wedge with low level northeast winds and
likely mostly cloudy skies. Thus, although temperatures will be
warmer, they will still likely stay just below normal in the upper
50s to lower 60s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A zonal flow will prevail over much of the United States early week
through mid week, setting up a period of quick moving systems and
associated fronts shifting across the Southeast. Expect the first of
two fronts to push through the area on Monday with potentially some
showers over parts of the area. Tuesday will be relatively quiet and
dry while a light southerly wind develops ahead of the next
approaching front. On Wednesday, a more significant cold front will
sweep through the area with showers. Dry and cooler high pressure
will then extend across the region on Thursday.

Overall high temps should range in the upper 60s to lower 70s
Monday, then low/mid 60s Tuesday and Wednesday. By Thursday, high
temps should only peak in the upper 40s to lower 50s. Overnight lows
will generally range in the mid/upper 40s away from the coast Monday
and Tuesday nights. Wednesday night lows should range in the
mid/upper 30s inland to low/mid 40s near the coast.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
VFR conditions will prevail at the CHS and SAV terminals through 06Z
Saturday.

Extended Aviation Outlook: Mainly VFR.

&&

.MARINE...
Tonight: A large region of arctic high pressure will continue to
build from western Canada and the Great Plains. Cold advection
continuing to surge in, steady isallobaric pressure rises and
geostrophic winds of 25 or 30 kt will produce northerly winds as
high as 20-25 kt over northern South Carolina waters and offshore
Georgia waters, where Small Craft Advisories remain in effect. While
a few gusts near 25 kt are possible beyond 15 nm for the remainder
of the coastal waters, the coverage and frequency is too limited to
hoist advisories. Seas will build as high 4-5 ft in nearshore waters
and 6-7 ft in the offshore Georgia waters. In Charleston Harbor
winds will flirt with advisory conditions, but will remain just shy
through the overnight period.

Friday...Marginal small craft conditions expected to end by
afternoon as cold high pressure continues building from the
northwest.

Saturday...No highlights as high pressure builds just north of the
waters. North-northeast winds of generally 15 knots or less and seas
4 feet or less.

Sunday...A weak coastal trough of low pressure is expected to slowly
move up the coast and then dissipate by late day. Other than the
potential for scattered showers, no highlights expected as winds
veer to east-southeast. By sunday night, models are showing winds to
increase from the south, but not thinking they will reach small
craft levels.

Monday...Southwest winds of 15 to 20 knots possible ahead of the
next cold front, expected to move through by late afternoon/evening.
Not much moisture again with this front, with slight chance for
showers.

Tuesday...High pressure returns north of the area with north-
northeast winds of mainly 15 knots or less and seas 2 to 4 feet,
highest offshore.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 2 PM EST this afternoon for AMZ374.
     Small Craft Advisory until 11 AM EST this morning for AMZ350.

&&

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



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