Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 242317
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
717 PM EDT Sat Sep 24 2016

.SYNOPSIS...
High pressure will build into the area Sunday but will weaken by
late Monday ahead of an approaching cold front. The front will
cross the forecast area and push off the coast by mid week and,
high pressure build into the region by the end of the week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Isolated shower activity that formed along the sea breeze earlier
has dissipated and expect dry conditions to prevail most areas
overnight as high pressure builds south. The latest runs of the
RAP and H3R both show isolated to scattered showers developing
along the Georgia coast prior to sunrise along what appears to be
a 925-850 hPA moisture channel that sets up in response to the
flow becoming increasing anticyclonic with time. Weak coastal
speed convergence that develops within this moisture channel may
be sufficient enough to produce said activity, but confidence in
its development rains low. Will continue to monitor short term
model trends and make further adjustments to the pop forecast if
needed. Conditions look to favor patchy fog development inland.
Lows from the upper 60s well inland to the mid 70s at the beaches
look reasonable and were maintained.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday and Sunday night: The pattern aloft will feature a high
amplitude ridge across the eastern third of the country with a weak
upper low undercutting the ridge and meandering to the west. At the
surface, high pressure will shift into the northeastern part of the
country and will build into the Carolinas through the day. This will
help set up a prevailing onshore flow through the day. Model time
heights and soundings show that moisture will increase in the lowest
5 kft within the onshore flow, but mid and upper levels will remain
relatively dry. Better moisture will be in place across southeast
Georgia and that is where the best PoP`s are in place, though they
are still in the 20-30 percent range. Have continued to carry a
slight chance of thunder, though profiles are very unimpressive.
Highs should range from the mid 80s at the coast to the upper 80s
further inland. Overnight, the inland ridge of high pressure will be
at its strongest and there are hints of a sharpening coastal trough.
Rain chances will primarily align along the coastal waters with the
chance for a few showers to brush the coast. Expect another mild
night with low 70s in most areas.

Monday through Tuesday: As the high to the north slips off the
coast, it will push a cold front into the Carolinas near the state
line. The region will stay within the onshore flow regime, and
moisture looks deeper through the column. Coverage of showers and a
few thunderstorms will be better, but the overall risk of severe
weather will remain low. By Tuesday, a cold front will push in from
the west and the low level convergence will improve with the front
in the vicinity of the forecast area. Again, most of the activity
will be showers, but there is enough instability to produce a few
thunderstorms. Temperatures remain above normal with mid 80s just
about everywhere.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Global models are coming into better agreement with the passage of a
cold front Wednesday night. Will keep chance POPs in the forecast
Wednesday and Wednesday night to account for possible showers and
thunderstorms ahead of and along the front. Cold air advection
ensues Thursday as mild continental high pressure builds in and the
cold front stalls to our south and west. Comfortable temps and dry
conditions are expected Thursday and Friday, though the close
proximity of the front adds some uncertainty to this forecast.

&&

.AVIATION /23Z SATURDAY THROUGH THURSDAY/...
Synoptic conditions do not looks as favorable for widespread
stratus development compared to previous nights. However,
some low-stratus could still develop, but will not be as
concentrated. Will limit the KCHS terminal to SCT004 with the
potential for light fog prior to sunrise, but trends will need to
be monitored for possible inclusion of IFR or LIFR cigs later. At
KSAV, a 2000-5000 cloud deck should preclude fog/low-stratus
development, but if this deck does not materialize as expected,
the risk would increase. Again, will need to monitor trends before
committing to IFR conditions. VFR will prevail for the remainder
of the 25/00z TAF cycle.

Extended Aviation Outlook: Flight restrictions will be possible each
morning through mid week each morning for possible stratus/fog
development. Also, showers and isolated thunderstorms could cause
brief reductions in ceilings and visibility, mainly in the
afternoons.

&&

.MARINE...
Tonight: Lowered winds by about a category all legs based on the
latest model data. Look for east to northeast winds <10 kt with
seas 2-4 ft.

Sunday through Thursday: High pressure will set up inland Sunday and
Monday, with a sharpening coastal trough Sunday night. Northeast
winds could surge into the 15-20 knot range at times, but should
stay below Small Craft Advisory thresholds. A cold front will
approach on Tuesday and finally push off the coast by mid week. No
significant increase in winds is expected through the end of the
forecast period. Seas will generally range 2-4 feet through early in
the week thanks to some lingering swell from Karl in the open
Atlantic.

&&

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

&&

$$



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