Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240005

Area Forecast Discussion
National Weather Service Charleston SC
705 PM EST Fri Feb 23 2018

Unseasonably warm high pressure will prevail into Sunday. A
cold front will approach the region late Sunday before moving
through Monday. High pressure is then expected until a warm
front moves through Wednesday or Wednesday night followed by
another cold front late in the week.


Early this evening: Not to sound like a broken record, but fog
and stratus are the main forecast issues for tonight. Similar to
the last few nights, there is a wide spread in the guidance and
some model sources are hard to trust given that they already
show a considerable amount of fog occurring over portions of the
coastal waters. Satellite imagery and web cams indicate that
fog/stratus is not currently going on, so we are starting with a
clean slate. Model consensus seems to be hitting southeast
Georgia harder with the fog potential and winds tonight will
closer to due south, so that seems to have some support. The 00z
KCHS RAOB came back with 16 knots of flow at 1 kft, which is a
few knots stronger than previous nights, so perhaps chances are
lower along for the Charleston area. Made some adjustments to
the coverage and descriptors for fog tonight, going with areas
of fog for most of the area outside of the Tri-County region.
The potential for locally dense fog is certainly there, but it
is near impossible to have enough confidence on where and when
to mention it in the forecast.


A summer-like pattern will prevail into Sunday ahead of a cold
front which will approach late Sunday. Temperatures will be well
above normal through Sunday with low rain chances until
possibly late Sunday across inland areas where deeper moisture
and better forcing will align. Rain chances will likely peak
Sunday night and/or Monday as the front moves into the area
along with deeper moisture and some upper-level forcing,
although timing of this is a bit tricky given the uncertainty in
timing of upper-level forcing. The front looks to be fairly
weak, as well as the instability, so do not anticipate much
rainfall or even significant thunder potential. Generally rain
amounts should be a quarter of an inch or less, but some places
could pick up a bit more, mainly closer to the Pee
Dee/Midlands/CSRA. Also, conditions will support late
night/early morning fog through at least Saturday, some of which
could be dense. By Sunday, low-level winds will be stronger and
less supportive of fog. The potential fly in the ointment
though would be if sea fog develops over the Atlantic and moves
inland well beyond the morning hours pretty much either day over
the weekend.


A cold front will move offshore Monday night. High pressure
will pass to the north Tuesday, then move offshore Tuesday
night. A weak warm front may develop over the area Wednesday,
followed by a cold front approaching from the west on Thursday.


KCHS: The overall set up is nearly identical to last night,
with perhaps a little better moisture in place. Therefore, the
forecast is similar with a slightly earlier starting time with
the arrival of MVFR ceilings at 09z and then IFR 1-2 hours
later. Included a TEMPO group to account for visibility drop
around sunrise. VFR conditions should return by mid morning.

KSAV: The overall set up is nearly identical to last night,
with perhaps a little better moisture in place. Model guidance
consensus is hitting the Savannah area harder with fog than
other locations. The forecast is similar, though it does
introduce the transition to MVFR and then IFR a few hours
earlier. Also included a longer TEMPO group for visibilities
below a mile around sunrise time. Fog could certainly become
dense, but confidence remains low. VFR conditions should return
by mid morning.

Extended Aviation Outlook: Flight restrictions are likely each
night/morning due to low clouds/fog into Sunday. The risk for
restrictions will increase Sunday night/Monday as a cold front
moves into the area with low clouds/rain.


Through tonight: No highlights. East-southeast winds will of 5
to 10 knots will persist through the period. Isolated showers
possible, mainly beyond 15-20 nm offshore. There is a small
potential for some sea fog late tonight, mainly the near shore
waters south of the Savannah River, but confidence not high
enough to put in forecast. Fog expected over the land will
likely get into the immediate nearshore waters late tonight.

Saturday through Wednesday: Atlantic high pressure will persist
across the area through the weekend. The pressure gradient will
increase a bit as a cold front approaches but winds will mainly
stay below 20 kt. However, southeast swells will continue and
could push seas up near Advisory levels toward the Gulf Stream.
Otherwise, warm and moist air will remain in place and could
lead to the development of sea fog across the cooler nearshore
waters through this weekend. Northerly winds will then develop
by Tuesday behind a passing cold front and could increase close
to Advisory levels. Seas will also build, possibly reaching
Advisory levels beyond 20 nm.


Record highs for February 23:
KCHS: 81/2012 and previous (broken today)
KSAV: 84/2012
KCXM: 78/1980

Record highs for February 24:
KCHS: 81/2017
KSAV: 86/2012
KCXM: 81/1930

Record high minimums for February 25:
KCHS: 62/1992
KSAV: 63/1992
KCXM: 61/2017

Record highs for February 25:
KCHS: 81/2017
KSAV: 82/1985
KCXM: 80/1930





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