Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 060326
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1026 PM EST Mon Dec 5 2016

.SYNOPSIS...
A storm system will affect the area through Tuesday evening. A
strong cold front will sweep through Thursday night followed by
cold high pressure through early next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Stationary front across southern GA this evening will move
northward overnight as a warm front due to increasing
southerly winds ahead of surface low pressure over LA which
will be moving northeast into TN by daybreak. This will allow
the high pressure wedge to give way over southeast SC/GA and
bring warmer and more unstable air into far southern SC. Strong
upper divergence, shortwave energy, deep moisture and the warm
front will make for welcome moderate to occasionally heavy
rainfall with many areas likely to see 1.5 to 2 inches through
daybreak. Chances for thunderstorms will also increase from
south to north as instability increases, mainly over southeast
GA. Despite minimal instability, a few storms could become
strong to possibly severe given the very strong low- mid level
wind shear and elevated low-level helicity associated with the
warm front. Damaging winds and/or tornadoes are the main threats
with any severe storms that track into the area from the south
and/or develop over the area.

Temperatures will generally remain steady and/or rise slowly
as the warm front lifts northward. Thus, low temperatures will
occur this evening for most locales, mainly mid to upper 50s
north and west and lower 60s southeast.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: A surface warm front should be located along the South
Carolina coast then extending westward into interior portions of
Georgia shortly after day break. The warm front is then expected to
slowly develop northward and should be north of the area by the
afternoon as an area of surface low pressure moves from the Midlands
into the Pee Dee region of South Carolina. Widespread rain with some
embedded thunderstorms is expected to be ongoing early Tuesday
morning, but as the upper level short wave lifts northeast of the
area by the afternoon, isentropic assent greatly diminishes, and the
deep level moisture gets shunted northeast away from the area, the
widespread rain should end from southwest to northeast. The warm
sector should overspread most if not all of the area in the wake of
the warm front and ahead of the cold front. With some CAPE values up
to 600 J/KG in the warm sector, cannot rule out a couple of
thunderstorms. However, limiting factors for thunderstorm
development are the dry air in the mid levels of the atmosphere and
only modest convergence along the front. Have lowered rain chances
in the afternoon, but it is quite possible that nothing develops
behind the departing area of rain. For any thunderstorms that
develop in the warm sector, there is a small threat that a storm or
two could become severe with strong damaging winds the most likely
threat. Very small chance for a brief tornado, but with decreasing
low level helicity values during the day it appears quite unlikely
that the best instability will coincide with the best helicity,
thereby making the threat very low. Assuming everyone gets into the
warm sector, highs will range from the lower 70s in the northwest to
the upper 70s in the south.

Tuesday night: Any lingering showers during the evening will quickly
come to an end. Skies should become partly cloudy with lows by
Wednesday morning mainly in the lower to mid 50s. There could be
some areas of fog around by daybreak Wednesday.

Wednesday through Thursday: Weak high pressure builds in Wednesday
through Thursday with cooler temperatures and dry weather. A strong
cold front is expected to move through the area by late Thursday
afternoon. At the present time, limited moisture should result in
nothing more than some cloudiness associated with the cold
front.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A mainly dry cold front will sweep through the area Thursday
night followed by cold and dry high pressure through early next
week.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Very poor conditions expected into Tue afternoon as a storm
system affects the area. Abundant moisture and moderate to
occasionally heavy showers will lead to low ceilings and
visibilities, at least in the LIFR range most of the time.
Expect improvement Tuesday afternoon, with VFR likely by 21Z at
KSAV and soon thereafter at KCHS. Instability will be weak
overall but cannot rule out thunderstorms, especially at KSAV
after 06Z and 12Z at KCHS. However, chances too low to mention
just yet. Lastly, an increasing low- level jet along with
generally light surface winds could lead to LLWS, mainly from
about 06Z through 15Z, but confidence low enough to preclude
mention at this point.

Extended Aviation Outlook: Sub-VFR conditions possible late
Tuesday night into early Wednesday associated with fog and/or
low ceilings. VFR conditions return Wednesday and then likely
persist into the weekend.

&&

.MARINE...
Tonight: Mainly northeast to east winds will prevail for the
first part of the night ahead of an approaching warm front from
the south. Widespread precipitation will spread northward across
the local waters, locally heavy at times, with a few
thunderstorms possible especially over the GA waters. A few
storms could become strong capable of producing damaging winds
and/or waterspouts. Winds will become southerly most waters and
increase after the warm frontal passage, reaching 15-20 kt,
especially beyond 20 nm where the best low-level instability and
mixing will be found. Seas will build toward 3-4 ft by sunrise,
highest near and beyond 20 nm. In addition, sea fog could
develop over the cooler near shore waters toward daybreak as
warmer and moister air moves into the area. However, the
rainfall will likely be more of a hindrance to visibility so we
did not mention fog explicitly in the forecast.

Gusty southwest winds and seas rising above 6 ft will yield Small
Craft Advisory conditions for the GA offshore waters Tuesday into
Tuesday evening. A small craft advisory is in effect for this area.
Conditions will be close to Small Craft Advisory levels in the outer
portions of the South Carolina near shore waters Tuesday, especially
for the waters off the Charleston County coast. However, given the
cool waters in a warm advection pattern, feel that limited mixing
should preclude winds and seas from reaching the Small Craft
Advisory criteria levels.

Tranquil conditions will develop across the waters by Wednesday
morning and then persist well into Thursday as weak high pressures
develops across the area.

Thursday night through Friday night will feature strong winds in the
wake of a strong cold front that moves through. Strong offshore flow
with cold advection will likely result in advisory conditions across
most if not all of the waters.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from 7 AM to 11 PM EST Tuesday for AMZ374.

&&

$$
NEAR TERM...RJB
SHORT TERM...MTE
LONG TERM...JRL
AVIATION...MTE/RJB
MARINE...MTE/RJB



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