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afdchs

Area forecast discussion
National Weather Service Charleston SC
956 PM EST Fri Nov 24 2017

Synopsis...
a cold front will shift through the area late Saturday night
followed by mainly dry high pressure into the middle of next
week.

&&

Near term /until 6 am Saturday morning/...
a frost advisory has been posted for all inland zones, including
tidal Berkeley, for early Saturday.

Clear skies within a decoupled boundary layer are promoting
quick temperature falls this evening with 25/02z temperatures
running several degrees cooler than even the coldest available
guidance. Winds are still slightly up along mainly the lower
South Carolina coast and parts of the immediate Georgia coast,
but this should change over the next few hours as the pressure
gradient continues to relax in the wake of departing low
pressure offshore. High resolution temperature guidance
continues to trend slightly colder with each passing run and
given current observed temperature trends, overnight lows have
been lowered by several more degrees. The updated forecast shows
lows Saturday morning bottoming out in the mid 30s across much
of the interior with coastal areas leveling off into the lower-
mid 40s, except upper 40s/near 50 right along the beaches.

The risk for frost is increasing and the latest trends suggest
the risk scattered frost will be highest roughly along/west of
a Huger-Summerville-Pocotaligo-Hardeeville-Port Wentworth-
Richmond Hill-Riceboro-Ludowici line, but away from the shores
of Lake Moultrie, including Pinopolis. A frost advisory has been
issued for these areas. Currently, the advisory does not
include the Charleston Metro area, but does include parts of the
Savannah Metro area. There is some concern that scattered frost
could reach as far east as the interior upper portions of
Charleston County near the Francis Marion as well as interior
lower Charleston County from Ravenel to Adams Run, but
confidence was not high enough to hoist an advisory in these
areas. Finally, would not be surprised to see a few sheltered
areas briefly drop to freezing just before sunrise.

&&

Short term /6 am Saturday morning through Monday/...
high pressure will slide east over the area this weekend with a
west/southwest flow contributing to noticeably warmer temps on
Saturday ahead of a cold front approaching from the
north/northwest. In general, Saturday afternoon highs should
peak in the upper 60s for most areas. A large mid/upper lvl
trough of low pressure will then expand over the east conus and
help push a dry cold front into the area Saturday night through
early Sunday. Temps will be cooler Post fropa as sfc winds turn
northerly and cold air advection takes place. Sunday afternoon
temps will struggle to warm into the lower 60s in northern areas
and into the middle 60s in southern areas under a full sun.
Areas will experience the coldest temps Sunday night, when
radiational cooling under clear skies favors overnight lows in
the mid/upper 30s away from the coast. Some frost is not out of
the question, especially for locations well inland in southeast
South Carolina. Sfc high pressure will then become centered just
north of the area on Monday, favoring a light onshore wind and
temps warming back into the middle 60s over most areas.

&&

Long term /Monday night through Friday/...
high pressure will generally prevail through Thursday, although some
coastal troughing could lead to a few showers starting Wednesday. A
cold front may cause more showers Thursday night and Friday.
Temperatures look to be at or above normal through the period.

&&

Aviation /03z Saturday through Wednesday/...
primary concern:
* none

VFR.

Extended aviation outlook: VFR conditions will prevail at both
terminals Saturday afternoon through Wednesday.

&&

Marine...
extended the Small Craft Advisory for the Georgia offshore
waters through 4 am.

Tonight: an area of weak low pressure is currently moving away
from the coast. At the same time, high pressure is located
inland. The interaction between these features is generating
northerly winds. The pressure gradient is forecasted to decrease
overnight and the result will be a downward trend in both winds
and seas, especially by daybreak.

Saturday through wednesday: high pressure will build over the
coastal waters this weekend, favoring northeast winds to become
primarily offshore by Saturday. A cold front will then push over
the coastal waters Saturday night into early Sunday,
temporarily increasing winds from the north as cold air advects
over the area. Winds could gust around 20 kts on Sunday, mainly
over South Carolina waters where mixing is strongest. Seas will
range between 2-4 ft. High pressure will then prevail into the
middle of next week with wind/seas that remain below Small Craft
Advisory levels.

&&

Chs watches/warnings/advisories...
Georgia...frost advisory from 1 am to 9 am EST Saturday for gaz087-088-
099>101-114>116-118-137-138.
SC...frost advisory from 1 am to 9 am EST Saturday for scz040-
042>045-047-052.
Marine...Small Craft Advisory until 4 am EST Saturday for amz374.

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