Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 060617

Area Forecast Discussion
National Weather Service Charleston SC
117 AM EST Tue Dec 6 2016

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.


Early this morning: Widespread light to moderate, with pockets
of heavy, rainfall continues across the forecast area. Near
daily high precipitable water values, in combination with a
large area of upper divergence in the right entrance region of
the 300 mb jet and strong low level convergence/frontogenesis
will continue to generate precipitation through sunrise. The
forecast area is still solidly wedged in as evidenced by surface
observations. The warm front is situated well to the south, just
north of the Florida/Georgia state line. As the parent surface
low lifts north into the Tennessee Valley, the warm front will
begin to push northward and attempt to scour out the cool wedge.
Models are mixed as to how quickly this occurs (which is
typical), but it will almost certainly be after sunrise.
Lightning observations show that virtually all of the thunder is
now confined to the coastal waters, though earlier we had enough
elevated instability for a few lightning strikes. Given that we
are expecting to stay solidly wedged through sunrise, the severe
threat is very low for now.


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


A mainly dry cold front will sweep through the area Thursday
night followed by cold and dry high pressure through early next


Solid IFR conditions are in place and will remain through at
least sunrise. Low ceilings and visibilities in the 2-4 mile
range will be prevailing conditions. A warm front to the south
will eventually push northward through the area, likely later
this morning. Once the front clears temperatures will rise and
there could be enough instability for thunderstorms. Confidence
is low so no thunder has been included, but it is possible. Once
the front moves through, ceilings may become more variable in
response to the increased convection and mixing. The mid and
upper levels will dry out late this morning and into the
afternoon and we should see clearing by early afternoon. IFR
conditions could linger until this point. This afternoon, expect
gusty southwest to west winds.

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.


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.


MARINE...Small Craft Advisory from 7 AM this morning to 11 PM EST this
     evening for AMZ374.



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