Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 180236
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
936 PM EST Sun Feb 17 2019

.SYNOPSIS...
An unsettled pattern is expected as a series of frontal systems
affect the area through next weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
18/02z mesoanalysis placed the warm front roughly along a
Millen-Estill-Ashepoo-Kiawah Island line. The front is moving
ever so slowly to the north and should push into the southern
Midlands and Pee Dee early Monday morning bringing the entire
forecast area into the warm sector. Overnight lows should occur
at most locations in the next few hours with temperatures
poised to rise into the mid-upper 60s by daybreak Monday. A cold
front approaching from the west will reach the far western
zones by sunrise. Isolated to scattered showers will accompany
the front. Pops 20-40% looks reasonable for the tonight period.

Sea fog continues to lurk over the Georgia and far southern
South Carolina nearshore waters late this evening. The fog has
spread inland across parts of the Savannah Metro Area and up
into Hilton Head. High resolution guidance still brings sea fog
as far inland as Walterboro and Moncks Corner by 1-2 AM as winds
turn more southernly, then scours the fog out thereafter except
right along the coast as low-level winds begin to increase.
This scenario seems reasonable given the current trends.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday: A weak cold front will be pushing through the area during
the morning, then offshore by afternoon. Moisture and large scale
forcing seem to be diminishing as this front pushes through.
Therefore, have maintained only low end chance PoPs for light
precipitation amounts. Despite the front moving through, high
temperatures are still expected to be quite mild, around 70, likely
helped by a little downslope flow.

Monday night: A strong wedge of high pressure develops north of the
area with increasing northeast low level winds. Deep layer moisture
begins to return/overrun the cooler low level airmass late, but only
have slight chance PoPs by late night south of the Savannah River.
Lows relatively mild, in the mid to upper 40s north and lower 50s
south.

Tuesday: A strong wedge of high pressure looks to hold north and
east of the area with northeast early, to east-northeast winds late.
Deep layer moisture continues to move northward and overrun the
lower level cooler air, while a weak coastal trough tries to develop
over the Atlantic waters. Models continue to differ a bit on precip.
chances, but have continued a slow trend upward from slight chance
to chance PoPs during the afternoon. Best chances expected to be
well inland and over the near shore waters in the coastal trough.
Highs expected to remain cool, in the mid 50s north to around 60
south.

Tuesday night and Wednesday: The surface wedge pushes off to the
northeast as a weak surface low pass well to the northwest. Deep
layer moisture and some upper level forcing should result in
scattered to numerous light showers, likely decreasing later in the
day on Wednesday. Temperatures Tuesday night in the mid to upper 40s
inland, warming to mid to upper 60s north and lower to mid 70s south
on Wednesday.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
The warm front will linger north of the area Wednesday night
through Friday while a series of upper shortwaves move through.
Isolated to scattered showers will remain possible. Temps will
be 10-15 degrees above normal due to strong warm air advection.
A cold front might sweep through late in the weekend.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
KCHS: IFR cigs will could improve if low-end MVFR by 05z as a
warm front lifts north. Risk for IFR cigs will still be present,
however. Will carry prevailing IFR through 05z, then TEMPO IFR
09-12z. FROPA looks to occur at 15z and could be accompanied by
a band of light rain. VFR will return by early afternoon Monday.

KSAV: Low cigs will persist for much of the night. Watching an
area of sea fog off the coast. There are signals some of this
could spread inland and impact the terminal over the next few
hours. Could see vsbys drop as 2 miles before visibilities
improve. Cigs should rise to MVFR around daybreak as a cold
front approaches. FROPA looks to occur at 15z and could be
accompanied by a band of light rain. VFR will return by early
afternoon Monday.

Extended Aviation Outlook:
Monday: Mainly VFR expected.

Late Monday night through early Wednesday: Periods of flight
restrictions, mainly due to low CIGS and possibly lower VSBYS with
fog.

Wednesday night through Friday: A return to mainly VFR conditions
expected.

&&

.MARINE...
Tonight: It is unclear exactly how far north the sea fog has
developed this evening with coastal webcams having gone dark
with the loss of sunlight. GOES-E fog products is also not
getting a good read with varying degrees of cirrus passing
overhead. Guidance certainly brings sea fog into the Charleston
Harbor and as far north as Bulls Bay after midnight, but am
hesitant to expand the Marine Dense Fog Advisory just yet until
additional observation data can be obtained. Otherwise, the
advisory remains in place until 1 AM for other 2 nearshore
zones.

Monday: No highlights expected as a weak cold front pushes through
the waters. Winds southwest at 15 to 20 knots ahead of the front in
the morning, veering to northwest 15 knots in the afternoon. Seas 3
to 4 feet, highest beyond 20 nm.

Monday night through Tuesday night: Small Craft Advisory conditions
expected as a strong high pressure builds north of the waters.
Sustained northeast winds will likely increase to around 20 knots
with gusts of 25 to 30 knots, with seas building to 5 to 9 feet,
highest offshore. Winds may decrease to 15 to 20 knots later Tuesday
night, but seas are expected to remain at advisory levels.

Wednesday and Thursday: Winds and seas are expected to fall below
advisory levels as the surface ridge pushes farther northeast and
the low level flow veers to east-southeast on Wednesday and
Wednesday night, then south-southwest on Thursday.

Sea Fog: Conditions may become favorable for more sea fog Wednesday
night and Thursday as the low level flow become southerly, which
will help to advect warmer, more moist air northward.

&&

.TIDES/COASTAL FLOODING...
Tide levels may reach marginal coastal flood advisory levels during
the Monday morning high tide, but winds will not be favorable, then
they will be parallel to the coast then offshore by afternoon. By
Tuesday and Wednesday, the low level flow is still expected to
increase from the northeast, strongest on Tuesday. Tide guidance is
still indicating coastal flood advisory conditions for both Tuesday
and Wednesday, mainly for the morning high tides.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Dense Fog Advisory until 1 AM EST Monday for AMZ352-354.

&&

$$


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