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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KCHS 230602
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
102 AM EST Sat Feb 23 2019

.SYNOPSIS...
A high pressure wedge will persist overnight into Saturday. A
warm front will lift north through the area Saturday into
Saturday evening. A cold front will move offshore Sunday and be
followed by high pressure into mid week. Low pressure will
impact the area late next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 1255 AM: Given a nearly saturated BL and broad isentropic
lift, rounds of drizzle or mist may pass over the forecast
before sunrise. Steady NE will advect lower dewpoints across the
SC Lowcountry and portions of SE GA. The wide dewpoint
depressions should reduce the fog potential. I will update the
forecast to add a mention of drizzle and adjust fog placement
and timing.

Previous Discussion:
Overnight: As a 1034 mb high builds south out of New York
state, the resulting cool air damming wedge will persist inland
between the coastal plain and the mountains. Considerable low
level moisture, the damp grounds and a feed off the Atlantic
will result in patchy to areas of fog, some of which will be
locally dense. We have expanded the coverage of the fog, mainly
over the coastal counties, and also allowed it to persist
through the night. Low stratus and a sharp inversion could allow
for a little fine drizzle at times as well. Otherwise our best
chance of any measurable rain will occur far northwest tier
where the best isentropic ascent will occur. Temps won`t fall
too much further through the rest of the night, but quite a bit
cooler than it was on Friday. Lows will range from the upper 40s
and lower 50s northwest to the mid and upper 50s southeast.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/...
Saturday: A warm front will lift north through the area during the
day into the early evening hours as the inland in-situ wedge
beings to break down in response to the transient parent high
shifting offshore the Mid-Atlantic states. As is typical with
eroding wedges, high temperatures will highly correlated to how
quickly the wedge erodes. Generally took a blend of the warmer
GFS with the cooler NAM to construct afternoon highs, but there is a
big bust potential here in some areas. Highs look to range from the
lower-mid 60s for areas adjacent to the southern Midlands and Pee
Dee to the upper 70s in the corridor of interior Southeast Georgia
bounded by I-16 and I-95. Guidance shows some weak isentropic assent
along/ahead of the warm front, but high condensation deficits
suggest measurable rainfall is unlikely. Saturday night looks quite
warm for late February as strong low-level jetting ahead of an
approaching cold front should keep the boundary layer well mixed.
Lows will only drop into the lower-mid 60s. Isolated showers are
possible overnight as pre-frontal warm air advection/isentropic
assent strengthens with the low-level jet. The cold front looks to
approach the far western zones by daybreak Sunday.

Sunday: A strong cold front is poised to push west-east across the
area as its supporting shortwave digs across the Great Lakes and
Ohio Valley. Moisture transport along/ahead of the front looks
pretty solid with southerly pre-frontal trajectories favoring
moisture advection off the Gulf of Mexico. Model cross-sections
suggest deep-layered DPVA/omega associated with the passing
shortwave and the right entrance region of the upper jet will pass
well to the north, but there is strong low-level omega signal from
the boundary later to H8 right along the front surface. This
suggests lift and associated rainfall will be primary confined to
the front itself and should manifest itself by a somewhat broken line
of showers moving from west-east during the day. Pops will be
confined to 60% area wide for now. Higher pops may eventually be
needed, especially across the far interior and the Charleston Tri-
County area where the low-level omega signal and moisture transport
is the strongest. Highs will warm into the mid-upper 70s with
temperatures falling as rain spreads east. Expect clearing and rain-
free conditions Sunday Night with lows ranging from the lower 40s
well inland to the upper 40s at the coast.

Monday: High pressure will extend across the region. It will be
considerably cooler with highs ranging from the mid 60s north
to upper 60s south; still slightly above climatological normals for
most areas.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Moderate to high confidence through Tuesday with low confidence
thereafter. Dry high pressure will likely persist through at least
Tuesday before a coastal trough and/or upper disturbance possibly
bring a chance of rain back to the forecast through mid week and
eventually a low pressure system later in the week. So chances are
pretty good that at least a portion of the mid-late week period will
be unsettled but timing and rain amounts are quite uncertain.
Temperatures should be near to above normal through at least
Wednesday before possibly dropping below normal.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
A strong low level inversion and broad weak forcing will
maintain IFR to LIFR ceilings across the terminals through the
6Z TAF period. Ceilings may improve to MVFR during the heat of
the afternoon, most likely at KSAV. Given a nearly saturated BL
and broad forcing, rounds of drizzle or mist may pass over the
terminals prior to sunrise. A warm front is expected to lift
across the region tonight, resulting in winds to shift from the
SE. Ceilings should gradually lower in the wake of the warm
front, the potential for fog will be greater after the 6Z TAF
window.

Extended Aviation Outlook: Restrictions likely Saturday night
into Sunday afternoon at KCHS/KSAV. Strong winds also possible
Sunday. More restrictions possible toward the middle of next
week.

&&

.MARINE...
Overnight: The modest NE pinching persists between an inland
wedge and the backdoor cold front south of the local waters and
continuing its trek southward. We have maintained a marginal
Small Craft Advisory (SCA) for the AMZ350 waters, and just below
SCA`s elsewhere. Fog and low stratus will be a continued problem
for mariners, resulting in areas of visibilities less than 1 nm
on the Georgia and lower South Carolina waters, with pockets of
visibility even lower. On the northern South Carolina waters
and in Charleston harbor we expect patchy fog with 1 to 3 nm
visibility to occur. There is probably too much wind for a Dense
Fog Advisory.

Saturday through Monday: Solid northeast winds Saturday morning will
gradually veer southerly through the day as a warm front lifts
north. Southwest winds will increase to 15-20 kt Saturday night as
pre-frontal low-level jetting intensifies. Cool shelf waters will
limit winds, especially over the Georgia nearshore waters.
By Sunday, winds and seas look to reach marginal Small Craft
Advisory thresholds over the Georgia offshore and Charleston County
legs with winds 20-25 kt and Seas 4-6 ft, while the other legs look
to fall just below this. Winds will veer west and eventually
northwest Sunday afternoon and Sunday night behind the cold front.
Could see some patchy sea fog develop Saturday afternoon across the
Georgia waters and spread into the South Carolina waters Saturday
Night. Winds look to be a bit too strong Saturday night to support
widespread development, but this will have to be watched. If any sea
fog develops, it will likely linger in some fashion until FROPA
Sunday afternoon. Benign weather will prevail Monday through
Wednesday.

&&

.CLIMATE...
Record Highs for February 24...
KCHS: 81/2017 and previous
KCXM: 81/1930 KSAV: 86/2012

Record High Mins for February 24...
KCHS: 60/1992 and previous
KCXM: 63/2018
KSAV: 64/1980

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 4 AM EST early this morning for
     AMZ350.

&&

$$
NEAR TERM...NED
SHORT TERM...ST
LONG TERM...RJB
AVIATION...NED
MARINE...
CLIMATE...