Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 241151

Area Forecast Discussion
National Weather Service Charleston SC
651 AM EST Wed Jan 24 2018

High pressure will prevail into Saturday, with a frontal system
to impact the area Sunday. Cooler high pressure will then
return for the first part of next week.


Today: The mid/upper levels consist of nearly zonal flow over
the Southeast U.S., with winds generally out of the west
southwest. A shortwave over the MS Valley in the morning will
move eastward, beginning to move overhead late in the
afternoon. This wave will bring an increase in high clouds
throughout the day. At the surface, continental high pressure
with it`s center over the Southern Plains this morning will
gradually move to the south and east. It`s eastern periphery
will dominate our weather pattern, bringing us dry conditions.
Cold air advection appears to be fairly weak, especially as
winds turn to the west this afternoon. Highs are expected to
rise to near normal. Though, if clouds are thicker than
expected, some minor adjustments might be needed with the

Tonight: The shortwave will be moving overhead in the early
evening, then shifting offshore during the overnight hours. The
associated high clouds will gradually decrease as the night
progresses. At the surface, high pressure centered over the
Southern MS Valley in the evening will move eastward, becoming
located over the Southern Appalachians late tonight. Again, the
eastern periphery of the high will influence our weather with
dry conditions. Models show cold air advection increasing as the
winds turn to the north late. Combined with the clear skies
late, the result will be temperatures a few degrees below
normal. If winds decouple in some spots, temperatures could be
colder than what is currently forecasted.


Thursday through Friday: Relatively benign weather will prevail, as
short wave ridging develops in wake of a short wave that moves
through early in the period, while surface high pressure covers much
of the east and southeast as it moves eastward late in the week. The
atmosphere is completely void of moisture Thursday with PWat less
than 1/4 inch, resulting in full sunshine throughout the day. Friday
will experience an increase in low level moisture as the synoptic
flow veers around to the E-SE. This along with isentropic ascent
will allow for marine-induced stratocumulus to advance onshore or
develop across the SE parts of our forecast district in the
afternoon. Temps will be near normal Thursday, then warming several
degrees Friday as H8 temps rise 2-3C and 1000-850 mb low level
thickness expands about 10-15 meters from the day before. In between
for Thursday night, good to excellent radiational cooling will
prevail allowing for lows 32-36F inland from the intra-coastal,
several degrees warmer along the barrier islands and in
downtown Charleston.

Saturday: A zonal W-SW flow will prevail aloft between a prominate
mid level ridge over the Bahamas and a strong short wave trough over
the northern Plains and upper MS River valley. We`re still under the
influence of expansive high pressure from the Atlantic, although the
anticyclonic circulation is slightly altered by a subtle coastal
trough not far offshore. This along with minor perturbations aloft,
better moisture in the 1000-800 layer and isentropic upglide
could support a small chance of showers in a few locations.
Considerable cloudiness will be counteracted by warm advection
as a modified marine air mass encompasses the area. So temps
look to reach into the mid and upper 60s away from the immediate


An amplifying mid and upper trough will sweep through the eastern
parts of the nation early next week, causing weak cyclogenesis
somewhere over or near FL along a cold front that approaches on
Sunday. Plentiful moisture will surge into the area Sunday as this
transpires, allowing for our best chance of wet weather this
forecast period. Instability is minimal, so no mention of thunder at
this time. Behind the cold front there is a shot of cooler and drier
Canadian air that moves in starting Monday.


VFR through 12Z Thursday.

Extended Aviation Outlook: VFR through Saturday. Potential for
flight restrictions Sunday as rain chances increase ahead of a
frontal system that impacts the area.


Today: Continental high pressure centered over the Southern
Plains this morning will gradually move to the south and east.
It`s eastern periphery will dominate the coastal waters with NW
winds in the morning shifting to the west in the afternoon.

Tonight: High pressure centered over the Southern MS Valley in
the evening will move eastward, becoming located over the
Southern Appalachians late tonight. Again, the eastern periphery
of the high will influence the coastal waters. Models show cold
air advection increasing along with some pinching of the
pressure gradient late. This will lead to winds shifting to the
north and increasing. At this point, it appears the waters
within 20 nm won`t need Small Craft Advisories. However, the GA
waters beyond 20 nm are borderline due to gusts approaching 25
kt. Given the short time period these conditions are forecasted
and the marginal confidence, we opted to hold off on an
advisory at this time.

Thursday: A 1035 mb high centered near the central Appalachians will
slide into eastern NC and VA during the afternoon. There is a decent
pinching of the gradient, and with cold advection and modest
isallobaric pressure rises in the morning we look to be close to
a marginal Small Craft Advisory on the outer GA waters.

Friday through Saturday:  A large region of high pressure over the
mid-Atlantic region Friday will shift offshore Saturday, as it
expands across the local waters. There might be a weak inverted
trough that forms inside the marine area, which prevent winds from
veering no more than to the E or E/NE. Winds are expected to remain
below 15 or 20 kt, but with the favorable onshore fetch there could
be a risk for a marginal SCA again on the AMZ374 waters, but this
time due to seas reaching near 6 ft.

Sunday through Monday: weak low pressure develops along a frontal
system over or near FL Sunday, before it shifts into the Atlantic
and is followed by continental high pressure building in for Monday.
Conditions remain below advisory thresholds Sunday, but cold
advection and isallobaric pressure climbs Monday could result in
SCA`s over parts of the marine district.


The KCLX radar remains out of service until further notice. Adjacent
radars include: KLTX, KCAE, KJGX, KVAX and KJAX.




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