Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 172048
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
348 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 /THROUGH TONIGHT/...
The area will remain in the warm sector ahead of an approaching
cold front. Diurnal cumulus will dissipate quickly this evening
with the loss of insolation with just thin cirrus traversing the
sky for much of the overnight period. Thicker cloud cover will
eventually develop from west-east early Wednesday as low
stratus develops and a thicker band of cirrostratus propagates
east. A stronger and more veered low-level flow suggests sea
fog influences will be considerably less than previous nights
and with increasing cloud cover late there are uncertainties on
whether any fog will develop at all. SREF fog probabilities
only max out into the single percentages and the latest RAP
soundings are far from showing an ideal fog environment. Opted
to remove all mention of fog except across interior Southeast
Georgia where several members suggest some fog could advect in
out of south-central Georgia just before sunrise. Low will drop
into the mid-upper 50s.

&&

.SHORT TERM /WEDNESDAY 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 MONDAY/...
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 /20Z TUESDAY THROUGH SUNDAY/...
VFR. Fog parameters are not has good as the past several days
with the low-level flow veering southwest versus south. Could
still see some shallow ground fog develop at both KCHS and KSAV,
but do not anticipate any major impacts at this time.

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 maintain the "areas of 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 Tuesday, 17 January:
KCHS: 78/2013 and previous years.
KCXM: 78/1928.
KSAV: 81/1943.

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.

&&

$$


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