Area Forecast Discussion
Issued by NWS Charleston, SC

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784
FXUS62 KCHS 200241
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
941 PM EST Sun Nov 19 2017

...SCATTERED FROST EXPECTED INLAND EARLY MONDAY...

.SYNOPSIS...
High pressure will prevail into Tuesday. Low pressure will pass
off the Southeast coast Tuesday and Tuesday night, followed by
additional low pressure systems late this week into next
weekend. A cold front will shift through the area by late next
weekend.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Expanded the Frost Advisory to include northern Tattnall, Evans
and northern Effingham Counties as guidance has lowered
slightly in these areas. Best chances for scattered frost is now
roughly along/north of a Reidsville-Claxton-Egypt-Cummings-
Walterboro-Jamestown line, but away from the shores of and
immediately downwind of Lakes Marion and Moultrie. Did opt to
nudge lows up a degree or two in the more rural areas of
Charleston County (mainly areas inland of Highway 17 and away
from the I-26/I-526 corridors), but do not anticipate scattered
frost in these areas. Still expect the coldest temperatures to
occur across far interior Southeast Georgia.

The main forecast concern continues to center on low temperatures
and the areal extent of frost formation across inland areas. A
fairly tight pressure gradient is expected to linger for much of
the evening hours before relaxing late as high pressure builds
east into the Deep South and post-frontal cold air advection
becomes neutral. Temperatures are still on track to bottom out
into the mid 30s well inland with upper 40s/near 50 at the coast
where temperatures will be tempered by the warmer maritime
environment as winds veer to the northeast prior to daybreak.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/...
Monday and Monday night: Ahead of an upper trough amplifying west of
the region, high clouds will increase Monday afternoon, and skies
will become mostly cloudy Monday night. However, sufficient dry air
should persist to maintain rain-free conditions through Monday
night. Monday high temps will range from the upper 50s north to the
mid 60s south. Monday night, low temps will range from the 40s at
most inland locations to the 50s on the beaches, where onshore winds
will persist. A few far inland locations, a longer period of thinner
clouds/radiational cooling could allow temps to briefly fall into
the upper 30s overnight.

Tuesday and Tuesday night: The deepening upper longwave trough will
promote surface cyclogenesis, and surface low pressure will eject
northeast from the Gulf of Mexico and will pass off the Southeast
coast. These systems will combine to support deep layered forcing
for ascent/coastal troughing and moisture transport, translating to
an increasing chance for showers across the area. Residual dry air
should initially limit the development/spread of precipitation
Tuesday morning, but moisture/precipitation should make greater
progress Tuesday afternoon when maximum POPs range from likely/high
chance near the coast to low chance well inland. Despite clouds and
showers, we continue to advertise high temps in the lower 70s far
south and mid/upper 60s elsewhere. However, if the SE to NW moisture
gradient does not evolve as expected and greater coverage of showers
pushes farther inland, temperatures well inland could struggle to
recover to 60F Tuesday afternoon. Then, the surface low will pull
away Tuesday night, and POPs will gradually diminish to slight
chance/chance from west to east.

Wednesday: Due to the continued presence/influence of the longwave
upper trough, maintained slight chance/chance POPs across the
region. However, give expected subsidence/drying in the wake of the
initial/exiting low pressure, feel that many locations, especially
across northern/inland counties, will remain rain-free Wednesday.
Expect high temps in the mid/upper 60s most locations.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
A strengthening upper shortwave over the northern Gulf of Mexico on
Thursday will lift northeast through Friday night, pushing another
surface low up the coast. A fairly sharp moisture/precipitation
gradient is possible with inland areas seeing little to no precip
while much greater coverage occurs over the coastal areas. Dry
weather currently anticipated next weekend. Below-normal
temperatures will prevail mid to late week, then near normal temps
could return next weekend.

&&

.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Primary concerns:
* None

VFR.

Extended Aviation Outlook: MVFR ceilings may develop late
Monday night and persist through Thursday. Brief vsby
restrictions in scattered showers late Tuesday through Thursday.

&&

.MARINE...
Tonight: High pressure will build from the north and west. This
will cause NW winds to shift to N and slowly diminish, although
still generally remain at least 15 kt for most of the waters
outside Charleston Harbor given the pressure gradient. Seas
will remain in the 2-4 ft range, highest beyond 20 nm.

Elevated northeast winds as high as 15-20 kt will prevail Monday
into Monday evening. Then, winds will slacken somewhat and will veer
toward the east/southeast for a time Tuesday. Seas of 2-4 ft will
prevail through this period. After surface low pressure passes over
or just east of the waters Tuesday night, winds will turn toward the
north/northeast, and the probability for SCA winds/seas will
increase mid to late week as the gradient tightens between inland
high pressure and offshore low pressure.

A series of high pressure systems will affect the waters next
week. An area of low pressure may shift up the coast Tuesday
into Wednesday, followed by another system Thursday into Friday.
A prolonged northeast gradient will result, with increasing
winds/seas mid to late week, potentially necessitating Small
Craft Advisories.

&&

.TIDES/COASTAL FLOODING...
Probabilistic extra tropical surge guidance advertises a Monday
morning high tide level close to 7 feet MLLW/1.24 feet MHHW in
Charleston Harbor, due in part to the lingering influence of the
November 18 New Moon and elevated northeast winds. Will continue to
assess the potential for brief, minor salt water flooding along the
South Carolina coast around the time of the 853 am EST high
tide.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Frost Advisory from 4 AM to 9 AM EST Monday for GAZ087-088-
     099>101-114-115.
SC...Frost Advisory from 4 AM to 9 AM EST Monday for SCZ040-042>045.
MARINE...None.

&&

$$



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