Area Forecast Discussion
Issued by NWS Charleston, SC

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310
FXUS62 KCHS 160553
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1253 AM EST Mon Dec 16 2019

.SYNOPSIS...
High pressure across the region today will slide offshore
through Monday. A cold front will then cross the area late
Tuesday, followed by high pressure into late next week. Low
pressure should develop near the coast next weekend.

&&

.NEAR TERM /THROUGH TODAY/...
Confidence continued to increase regarding the fog potential,
especially since there are already signs of it developing, plus
the low level winds are now forecast to be a little less than we
early thought. We have patchy fog early tonight, with coverage
increasing to areas of fog near and west of I-95 after 3 am.
Condensation pressure deficits are near zero across many areas,
which could result in patches of dense fog as we get closer to
daybreak.

Otherwise, clear skies overnight will give way to an increase
in stratus that occurs with the fog late and toward daybreak.
Winds will be light southerly or calm, but with warm advection
above the strong surface inversion, temps won`t be as cold as
last night. We`re carrying 40-45F far inland, 46-50F closer to
the coast, and a few pockets of upper 30s in the Francis Marion
Nat`l Forest.

&&

.SHORT TERM /TONIGHT THROUGH THURSDAY/...
Monday: The forecast area will remain between high pressure
centered over the western Atlantic and organizing low pressure
over the lower Mississippi River Valley. The sfc pattern will
support steady south winds by Monday afternoon, resulting in
rising llvl thicknesses through the day. The combination of
partly sunny conditions and mild low level thermal profiles
should yield well above normal high temperatures. I will
forecast low to mid 70s across the Charleston Tri-County to the
upper 70s across SE GA. Monday night, the center of the low is
forecast to track rapidly to the NE, reaching the mid-Appalachians
by dawn Tuesday. The associated cold front will cross the lower
Appalachians late Monday night, passing over the east facing
slopes by sunrise Tuesday. SPC HREF indicates that a patch of
pre-frontal showers will pass over the forecast area after
midnight, resulting in 0.15 of an inch or less. The arrival of
thick of mid and high clouds and steady south winds should limit
cooling to the upper 50s.

Tuesday: Short term guidance indicates good agreement with the
late afternoon to early evening passage of a band of convection.
GFS and NAM forecast a wide field of SBCAPE between 500-1000
J/kg along and ahead of the cold front. Given the instability, I
will maintain a mention of SCHC thunderstorms. SPC Convective
Outlook discusses the potential for one or two strong storms,
but confidence is too low to highlight with a Marginal risk at
this time. Using a blend of guidance, QPF on Tuesday is expected
to range from near a half inch inland to .3 of an inch along
the coast. Given the late day arrival of the showers/thunderstorms
and CAA, high temperatures should range within a degree or two
from values reached on Monday.

Wednesday: High pressure will increase across the forecast area
in the wake of the cold front. CAA is forecast to end during
the early daylight hours, with H85 temps remaining between 1-4C
through the rest of the day. The day should begin with
temperatures in the lower 40s across the forecast area. Given
mostly sunny conditions through the day, high temps should peak
in the low to mid 50s.

&&

.LONG TERM /THURSDAY NIGHT THROUGH SUNDAY/...
Dry and cool high pressure will persist across the Southeast United
States through late week. Light north/northeast winds will keep high
temps in the mid 50s Thursday while overnight lows dip into the
low/mid 30s away from the coast Wednesday night and Thursday night.
Temps will slowly warm into the upper 50s/lower 60s Friday as low
pressure develops off the Southeast Coast. Guidance suggests the
potential for precip to return across the area during the weekend,
mainly as the low deepens and tracks north/northeast offshore
Saturday into Sunday. Precip chances should be highest near the
land/sea interface Saturday. Temps should also peak in the upper
50s/lower 60s each day. Overnight lows should range in the mid/upper
30s inland to low/mid 40s near the coast.

&&

.AVIATION /06Z MONDAY THROUGH FRIDAY/...
VFR the first part of tonight and during the late morning and
afternoon Monday. However, from about 08-14Z conditions are
favorable for the development of fog and stratus. The model
consensus and climatology supports a better potential of KSAV
than at KCHS. On the 06Z TAFs, we introduced IFR vsbys at KSAV
but did not opt for any low cigs at this time. We maintained
MVFR vsby at KCHS around daybreak.

Extended Aviation Outlook: Flight restrictions are possible at both
terminals late Tuesday with the passage of a pre-frontal line
showers and thunderstorms. VFR conditions are expected across the
region Wednesday and Thursday.

&&

.MARINE...
We`ll need to carefully watch for fog developing in Charleston
Harbors late tonight into Monday morning. However, with an
onshore flow it looks like it should stay inland from the AMZ330
marine zone, mainly north of the Don Holt Bridge.

High pressure will remain across the near shore waters through
Monday. Winds during this time are forecast to continue from
the south between 5-10 knots with seas between 2-4 ft.

Late Monday night, sfc dewpoints and temperatures in the low
60s, nearly parallel near shore winds, sea sfc temps in the
upper 50s to low 60s, will favor the formation of sea fog during
the pre- dawn hours. I will add a mention of patchy fog to the
forecast. Southwest winds are expected to gradually strengthen
ahead of a cold front Tuesday. Small Craft Advisory criteria
wind gusts and seas will be possible over portions of AMZ350 and
374. A band of showers and thunderstorms will pass across the
waters late Tuesday into Tuesday night. In the wake of the cold
front, NW winds will increase with gusts to 25 kts across the
near shore waters Tuesday night into Wednesday morning. Small
Craft Advisory conditions may linger across the outer GA waters
through Wednesday. High pressure will increase over the waters
Thursday and Friday, supporting NE winds between 10-15 kts and
seas between 2-5 ft.

&&

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

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...



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