Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 180243
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
943 PM EST Tue Jan 17 2017

.SYNOPSIS...
Weak high pressure will move offshore tonight. A front will then
waver across the area through early next week, keeping conditions
unsettled.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Late this evening: Only minor updates to temperatures and
dewpoints based on recent observations. Previous discussion
follows below.

Early this evening: No significant changes to the going
forecast. The main forecast issue is the fog and stratus
potential. The environment is considerably different than 24
hours ago as prevailing southwest flow is in place and should
only strengthen through the night as the pressure gradient
increases ahead of a cold front to the west. In fact, virtually
all model soundings show winds in the surface to 1000 feet layer
increasing as high as 25-30 knots. This should provide
sufficient mixing to prevent fog development and the wind
direction will make it difficult for any sea fog that develops
to move onshore. Stratus could sneak in from the west late,
perhaps building down some fog, impacting mainly inland areas of
southeast Georgia.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday: A shortwave moving across the Mid-Atlantic states will
push a weakening cold front southward. The front is expected to pass
through the northern part of the area in the afternoon, then stall
across the southern portion of our area in the evening. The front
has very little moisture, so the forecast is dry with partly/mostly
cloudy skies. Compressional heating ahead of the front should allow
near record highs well into the 70s across the entire area, with 80
degrees not out of the question far south. Lows should generally be
in the 50s, aided by some clouds, especially across the southern
zones.

Thursday: Ridging builds over the east coast while surface high
pressure spreads in lee of the Appalachians. The front is forecasted
to slowly drift northward as a warm front through the day. Again,
minimal moisture will lead to a dry forecast. Highs will vary from
the mid 60s north (where the front reaches late) to the mid 70s
south (where the front will have moved northward of early in the
day). However, these temperatures are highly dependent on the
location and northward speed of the front. Slower/faster speed
could lead to colder/warmer temperatures across our northernmost
zones.

Thursday night into Friday: The ridge will shift offshore, dragging
the surface high with it. As the warm front moves north of our area,
weak low pressure is forecasted to develop well to our northwest,
then move towards the northeast. A cold front attached to this low
will gradually approach our area from the west. Deep moisture will
spread across the area behind the warm front and in advance of the
cold front. We have POPs increasing Thursday night into Friday with
the greatest risk being west of I-95. Some thunderstorms will also
be possible Thursday night into Friday, mainly in Georgia where the
best instability is expected. Severe weather is unlikely because
instability is not impressive. Despite the rain risk and cloudy
skies, warm air advection should allow temperatures to reach well
into the 70s.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
A wave of low pressure is likely to push off the NC coast Friday
night dragging a weak cold front into the area. The front will then
stall out with rain chances increasing from the south as deeper
moisture associated with an upper shortwave moving through the
region. The front will continue to be a source of low-level
convergence as it shifts northward as a warm front Saturday night
into Sunday and with deeper moisture returning to the area along
with strong forcing ahead of a deep upper low moving through the TN
Valley rain chances will be high and there will be a risk of some
stronger storms Sunday as the low-level flow increases along with
instability. Pretty good model agreement that the best rain chances
will be done by daybreak Monday with the cold front slowly pushing
through Monday, with breezy conditions expected. It will take some
time for the large upper trough to shift offshore so the coldest
temperatures will be delayed until Tuesday, although only dropping
to near normal levels.

&&

.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions are expected to prevail at KCHS and KSAV through
00z Thursday. Thanks to increased southwest winds in the lowest
500 to 1000 feet of the atmosphere, fog is not expected to be a
concern. Stratus may try to form to the west and push into the
vicinity of KSAV around sunrise, but the thinking is VFR will
prevail and have only advertised scattered MVFR clouds.

Extended Aviation Outlook: Flight restrictions are possible Friday
through Sunday due to a front wavering across the area.

&&

.MARINE...
Tonight: Primary concern is sea fog. The setup does not look as
favorable for sea fog development, mainly due to diminished
parcel residence times over the cool shelf waters. Best chances
for fog look to reside over the South Carolina nearshore zones
where parcel residence times will be the greatest. SREF fog
probabilities are not all that high, which leads to decreased
confidence. Will go with the "patchy fog" qualifier overnight,
but not mention any vsbys below 1 nm. Otherwise, south to
southwest winds <10 kt will prevail with seas 1-2 ft nearshore
and 2-3 ft offshore.

Wednesday through Sunday: No significant concerns regarding
winds/seas. Winds should briefly surge across the Charleston County
waters Wednesday afternoon as a cold front moves through, then
becoming stationary along our GA waters Wednesday night. Winds
should generally be light and vary as the front slowly moves
northward Thursday into Friday. Unsettled weather is expected into
the weekend.

&&

.CLIMATE...
Record highs for Wednesday, 18 January:
KCHS: 77/1952.
KCXM: 79/1928.
KSAV: 81/1937.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...BSH
SHORT TERM...MS
LONG TERM...RJB
AVIATION...BSH/MS
MARINE...MS/ST
CLIMATE...



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