Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
344 am EST Monday Dec 29 2014
a cold front will push south through the area late this afternoon
into tonight. High pressure will build into the area Tuesday into
Friday...before moving into the Atlantic by Saturday. A coastal
trough will develop early this weekend then lift north of the
region on Sunday. A cold front front will then pass off the coast
early next week.
Near term /through today/...
..difficult fog forecast this morning...
Through mid-morning...dense fog will remain a concern as
warm/moist air continues to advect northward into the region ahead
of an approaching cold front. Dense sea fog has encompassed much
of Charleston County and is bleeding into portions of Berkeley...
Dorchester and Colleton counties where widespread dense radiation
fog is also occurring. Visibilities have been near zero at times
per spotter and County warning point reports...but some
improvements in visibilities have been noted in the past 1-2 hours
at a few sites. It is unclear whether this is temporary improvement
or the beginning of a more definitive trend. Winds have increased
to as high as 20 knots atop the fog layer per kclx VAD wind profile
data and may be helping transition some of the fog into a very low
stratus deck. Rap 1000 feet winds are prognosticated to increase to 25-30
knots by sunrise...so the fog forecast is certainly not clear cut.
Farther south...satellite and surface observations show a large
area of sea fog and low stratus with origins from the northeast
Gulf of Mexico is poised to move north of the Altamaha river
through sunrise. Visibilities may very well drop below 1/4 mile
across parts of southeast Georgia and the remainder of southeast
South Carolina over the next few hours as some stratus build down
occurs. Trends are being watched for a possible expansion of the
dense fog advisory. Again...it is unclear how the increase in 1000
feet winds will affect the fog potential in this area.
Shower activity associated with a weak area of warm air advection
ahead of an approaching cold front will largely remain west of the
area through mid-morning.
Rest of today...a wave frontal wave and cold front will drop south
into the area today shear shortwave energy passes off to the
north. Deep moisture coupled with anafrontal upglide as well as uvm
induced by the right entrance region of a 110 knots jet streak will
support scattered to numerous showers this afternoon. Models are
similar in showing little in the way of measurable rainfall
through late morning with activity blossoming over much of
southeast South Carolina and southeast Georgia during the middle-late
afternoon as the ribbon of strong jet dynamics passes overhead.
Will highlight likely probability of precipitation today of 60-70 percent. Despite the
warm temperatures...the atmosphere looks too moist and stable to
support much of the way of thunder for much of the day. The only
exception would be in a narrow corridor just ahead of the cold
front from roughly Ludowici to Savannah...Hilton Head and points
south where nam12/GFS boundary layer lifted index and 850 hpa
showalter fields suggest there may be just enough surface and
elevated instability to support an isolated thunderstorm or two. Highs
will range from the middle 60s well inland to the upper 60s to lower
70s across the coastal counties with a few middle 70s across McIntosh
Short term /tonight through Thursday/...
tonight...the weak cold front will drop south through the area
overnight. The best chance for rain will occur this evening as the
last of the sheared shortwave energy passes offshore and to the
north. The primary frontal band rain activity will gradually
dissipate with time as the front shifts south and offshore. Will
carry 50-70 percent probability of precipitation during the evening hours...highest across
the coastal counties...with probability of precipitation steadily diminishing through the
night as the front clears the area and middle-level dry air
advects in from the southwest. Lows will range upper 40s well
inland to the upper 50s along the Georgia coast.
Tuesday...the cold front is expected to be offshore extending back
into NE Florida during the morning. There could be areas of low
clouds in the frontal trough before stratocumulus expand during
the day. Models indicate a fast mainly zonal flow aloft with a
buckled surface pattern to the Lee of the mountains as cold air
advection builds across the Carolinas. Weak downslope and slower low
level cold air advection pattern in southeast Georgia suggest milder temperatures
with some afternoon clearing possible. To the north...we maintained
plenty of clouds across South Carolina and keep probability of precipitation silent. Some
upper forcing may lead to a few sprinkles northern zones but the
deeper layers look too dry to keep any lingering probability of precipitation. We lowered
high temperatures over far northern zones due the expansive clouds and
colder boundary layer temperatures.
An impressively strong and expansive surface high will stretch
across much of the central and eastern United States Wednesday
and Thursday. Expect rather quiet conditions to prevail...with
temperatures not far from seasonal normal. High temperatures will
be in the middle 50s north to near 60 degrees south under mostly clear
to party cloudy skies. Both Wednesday and Thursday morning will
feature lows in the lower to 30s inland to upper 30s to near 40
along the U.S. 17 corridor.
Long term /Thursday night through Sunday/...
the expansive surface high will steadily shift over Georgia and
the Carolinas by Friday...before moving into the Atlantic waters
Saturday. A strong cut off low over the Desert Southwest Friday will
eject into the Southern Plains over the weekend and then dampen
as it move into the upper Gulf Coast region by late weekend. Clouds
will be on the increase Thursday night as a short waves traverses
into the region atop a large subtropical ridge over Florida and
the Caribbean. This disturbance may produce some spotty light rains
on Friday but certainly not significant as precipitation is likely to
evaporate in dry layers below 10 kft. A slight chance pop looks quite
sufficient. Steadier rains across north Georgia and the western
Carolinas may begin to anchor a wedge on Saturday with global
models differing on surface patterns. The weekend looks a bit
unsettled with plenty of clouds most areas and mainly low end chance
probability of precipitation as the upper wave flattens significantly late in the weekend.
Sunday appears to be the warmer of the days after we trended down a
good bit on temperatures northern zones Saturday. A cold front should move
off the coast early next week.
Aviation /07z Monday through Friday/...
kchs..vsbys are steadily lowering as a combination of radiation
fog and possibly sea fog affects the terminal. Expect conditions
to drop below Airport minimums soon with visibilities dropping to 1/4sm
vv001 and staying there through about 13-14z. There may be some
variable visibilities through about 08z...but should settle well into
LIFR after that. Conditions will improve to MVFR 14-16z and remain
there through sunset. Light rain will likely impact the terminal
21-02z as a cold front drops south. Visibilities will be limited to MVFR
for now...although periods of IFR are possible in pockets of
heavier rainfall. Low clouds will fill back in behind the front
with IFR ceilings.
Ksav...difficult fog forecast for the terminal with high resolution
models offering a number of possible outcomes. Will continue to
stay somewhat conservative until more pessimistic trends become
apparent...but it is certainly possible conditions could drop below
alternate minimums and even Airport minimums prior to sunrise. For
now will limit conditions to 2sm br ovc006...or just above
airfield minimums. Amendments will be issued as needed. Expect MVFR
conditions to return by 14z. Light rain will overspread the
terminal by 20z and linger through 03z as a cold front drops
south. Expect IFR ceilings to fill in behind the front.
Extended aviation outlook...flight restrictions are likely late
tonight as a cold front moves across the region. MVFR ceilings
possible into the day Tuesday in the wake of the front...VFR
conditions return Tuesday night into late week.
today...dense sea fog will linger or much of the day across the
coastal waters. The fog will likely retreat a bit through the day
into the corridor of coldest water location from the beaches to
about 5-8 nm offshore. Will maintain the marine dense fog
advisory for all legs except the Georgia offshore waters through
10 am. Otherwise...SW winds around 10 knots will persist with
combined seas averaging 2-3 feet nearshore and 3-4 feet offshore.
Tonight...the risk for sea fog will linger through this evening
over the South Carolina waters and late tonight for the Georgia
nearshore waters as a cold front drops south. As winds turn north
any sea fog could be pushes to the south and offshore. SW winds
5-10 knots will prevail ahead of the front...then turning north 10 knots
with its passage. Seas will 2-3 feet will subside to 1-2 feet over the
nearshore waters with 3-4 feet seas subsiding to 2-3 feet for the
Georgia offshore leg.
Tuesday through Friday...high pressure will build from the northwest
middle week and reside over the waters by Friday. Cooler and quite a
bit drier air moving in will set up some tight thermal and
moisture gradient Tuesday night into Wednesday night resulting in
some occasional surges from the north and northeast. 15-20 knots flow
over the Georgia waters on Wednesday should result in seas
building to 4-6 feet beyond 20 nm offshore. Small Craft Advisory
conditions are possible during this time. Lighter winds by late
week with winds and seas below any criteria thresholds. A bit too
early to commit on strength of The Wedge this weekend and timing
the warm front through...but complex low level mixing environments
SC...dense fog advisory until 10 am EST this morning for scz043>045-
Marine...dense fog advisory until 10 am EST this morning for amz330-350-