Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 082107

Area Forecast Discussion
National Weather Service Charleston SC
407 PM EST Thu Dec 8 2016

Cooler 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.


A broad upper level trough will continue shifting eastward
toward New England while a surface cold moves offshore. Winds
have shifted to the NW across our entire area and high clouds
associated with the front are currently floating overhead. Cold
air advection, drier air, and gradual clearing are expected
overnight. Lows will range from the mid 30s inland to around 40
degrees at the immediate coast.


Overview...This period will be marked by much colder temperatures,
with below normal temperatures, with low temperatures about 10
degrees below normal. No significant precipitation is expected through
the period.

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.


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.


VFR at CHS and SAV through 18Z Friday.

Extended Aviation Outlook:

Friday and Saturday...VFR expected.

Sunday...With a developing coastal trough there could be brief
flight restrictions due to lower ceilings, mainly at KCHS. Otherwise
VFR expected rest of Sunday and into early Monday.

Monday...Brief flight restrictions again possible with the next cold
front and small chances for showers/light rain.

Tuesday...VFR expected to prevail.


Tonight: NW winds will increase to a fresh breeze this evening
and overnight as a cold front moves through the waters. Strong
cold air advection behind the front will produce gusts around
25 kt across the outer portion of AMZ350 and for all of AMZ374.
Small Craft Advisories remain in effect for these zones. Wind
gusts to 25 kt are expected around 20 nm out for AMZ352-354.
Given the limited areal coverage, we opted to hold off on
issuing advisories for these zones. However, if the areal
coverage increases, then advisories may be needed for one or
both of these zones. As for seas, they will build to near 5 ft
beyond roughly 15 nm out and 6-7 ft for AMZ374.

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

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

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.


MARINE...Small Craft Advisory from 9 PM this evening to 2 PM EST Friday
     for AMZ374.
     Small Craft Advisory from 9 PM this evening to 11 AM EST
     Friday for AMZ350.


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