Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 200332
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1032 PM EST Mon Feb 19 2018

.SYNOPSIS...
A large area of high pressure will remain across the region for
much of the week. A cold front should approach the area early
next week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A continued feed of marine moisture stuck beneath a
strengthening nocturnal inversion, plus the already elevated
dew points as high as the lower and middle 60s, will lead to an
expansion of the stratus/fog already across our coastal zones.
With condensation pressure deficits less than 1 or 2 mb and
light or calm winds we have a Dense Fog Advisory in effect for
the entire forecast district through 10 am Tuesday. We start the
night with areas of dense fog over the coastal corridor, with
patchy fog further inland. Then we increase the coverage to
widespread dense fog everywhere after 1 or 2 am through the mid
morning hours on Tuesday. This is in line with all Hi-Res model
solutions and favored as per climatology with the onshore
trajectories.

There certainly could be some spotty drizzle overnight, but the
overall thickness to the stratus might be a little too thin for
it to occur.

On average lows will be in the upper 50s to near 60F, with a few
mid 50s close to the Santee River.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
The short term period will be dominated by a large ridge centered
between the Carolinas and Bermuda. In fact, GEFS normalized anomaly
of H5 and H7 heights will remain two standard deviations above
normal Tuesday through Thursday. To the west, a longwave trough will
remain over the western CONUS through the period. This pattern
should keep deep moisture generally limited to Mississippi basin.
Forecast soundings across the CWA indicate a very strong subsidence
inversion centered around H85, the strength of the inversion is
forecast to range from 4-6 degrees C. Below the inversion, southeast
winds will supply marine moisture across the forecast area,
especially near the coast. At night, the moisture will likely
support the formation of widespread stratus, with lowering cloud
bases through the night. The development and lowering of stratus
will be possible each night, resulting in late night to early
daytime fog. Daytime mixing may allow cloud cover to scatter during
the afternoon. However, cloud cover will be slow to dissipate from
morning stratus. Despite the cloud cover, a very warm thermal
profile should result in high temperatures to reach the low to mid
80s inland, in the upper 70s near the coast. These temperatures will
be near record levels, see climate section below. The strong capping
and lack of forcing will result in dry conditions through the short
term period.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
A large ridge of high pressure centered over the western Atlantic
will be the primary contributor to the weather over the Southeast
United States, allowing warm conditions to persist through the
weekend. In general, temps will be well above normal, peaking into
the upper 70s/lower 80s Friday, Saturday and Sunday. Overnight lows
will be mild, ranging in the upper 50s to lower 60s. The next chance
for more substantial shower chances should arrive late Sunday or
Monday as a mid/upper trough passes to the north with a southward
extending cold front that shifts through the Southeast. Once fropa
occurs, temps should be slightly cooler, peaking in the mid/upper
70s on Monday.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
KSAV: Satellite pictures showing the fog expanding up the
Savannah River from the Atlantic and spreading into the
airfield within an easterly flow. As the stratus and fog
increase in coverage through the night and the nocturnal
inversion strengthens and lowers, we are forecasting LIFR
conditions most if not all of the time through the middle of
Tuesday morning. Ceilings and visibilities will be at or below
airfield minimums during this time.

KCHS: Fog and stratus will become a problem tonight into
Tuesday morning, the result of a continued feed of low level
moisture onshore and a strengthening and lowering nocturnal
inversion. MVFR late this evening, will fall into the IFR or
potentially the LIFR range by late tonight through the middle of
Tuesday morning, before VFR returns. Dense fog is certainly
possible for several hours, especially from about 08Z through
1330Z Tuesday, and we could be close to or even below airfield
minimums during that time.

Extended Aviation Outlook: Fog and low ceilings may develop across
the region Tuesday night into early Wednesday morning. Patchy fog is
possible late Wednesday night. Otherwise, VFR conditions should
prevail.

&&

.MARINE...
Tonight: GOES-16 Night Fog satellite imagery (10.3-3.9 micron)
depicts the low stratus/sea fog extremely well, and that along
with a recent report of near zero visibility from the Savannah
Pilot Boat near Buoy Tango, we have a Dense Fog Advisory in
effect for all nearshore waters out 20 nm through 1 pm Tuesday.
Webcams and surface observations in and near Charleston Harbor
indicative of fog developing, and conditions will only get worse
through the night. Those waters also have a Dense Fog Advisory
in effect through 10 am Tuesday. The ports of Savannah and
Charleston will likely become closed at some point tonight.
Otherwise, under the influence of strong sub-tropical ridging,
there isn`t much happening regarding winds (E 5 or 10 kt) nor
seas (2-3 ft, with some 4 footers over AMZ374).

Monday through Saturday: Strong high pressure will remain over the
western Atlantic through late week. Warming dewpoints and a strong
low level inversion should yield marine stratus with fog over the
shelf waters through Thursday. Otherwise, the marine area should see
steady southeast winds and wave heights between 2-3 feet nearshore
and 4-5 feet across the outer GA waters.

&&

.CLIMATE...
Record Highs

Wednesday 2/21 CHS   82 1991
               SAV   83 1991
               CXM   80 2001

&&

.EQUIPMENT...
The downtown Charleston observation site (KCXM) has stopped
reporting. We are unsure when the data will be restored,
including the Climate data. But the data is still likely being
collected and is available for archive at the site, requiring a
tech to retrieve it manually at a later time.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Dense Fog Advisory until 10 AM EST Tuesday for GAZ087-088-
     099>101-114>119-137>141.
SC...Dense Fog Advisory until 10 AM EST Tuesday for SCZ040-042>045-
     047>052.
MARINE...Dense Fog Advisory until 1 PM EST Tuesday for AMZ350-352-354.
     Dense Fog Advisory until 10 AM EST Tuesday for AMZ330.

&&

$$
NEAR TERM...
SHORT TERM...NED
LONG TERM...DPB
AVIATION...
MARINE...
CLIMATE...
EQUIPMENT...



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