Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Charleston SC
351 PM EST Wednesday Nov 25 2015
strong high pressure will prevail inland through the weekend...as
a weak coastal trough lingers nearby late this week. The area of
high pressure will weaken somewhat next week as a cold front passes
by to the north.
Near term /until 6 am Thursday morning/...
broad surface high pressure will prevail to the north tonight
while the 850 mb ridge axis sits just off the middle-Atlantic coast.
Moderate easterly flow above the surface will maintain a weak
moisture flux into coastal areas. Thus far today the model sky
cover forecasts have been too bullish...likely due to the extent
of dry air in lower-levels. We do anticipate an increase in low
level cloudiness into coastal areas and farther into southeast Georgia
where deeper moisture is forecast to advect. However...farther
inland after some initial cirrus shifts out...we could have mostly
clear skies in place much of the night. We therefore lowered temperatures
far inland into the lower 40s with higher values closer to the
coast where winds are stronger and clouds are thicker. Even if
some temperatures drop a bit lower in sheltered locations like they did
this morning...occasional bursts of wind and very brief duration
of the colder temperatures should preclude any frost issues.
The weak moisture advection and isentropic ascent may support
isolated rain showers over the coastal waters tonight.
Short term /6 am Thursday morning through Saturday/...
an area of strong high pressure extending from south of Newfoundland
southwestward into the Middle Atlantic States will produce northeasterly
winds across the entire County Warning Area on Thursday with breezy conditions
near the coast. Clouds will be thicker closer to the coast where
the marine layer will be advecting onshore...and there will be a
slight chance of light showers for the coastal counties as
well...although any rainfall amounts will be minimal. Highs should
reach the lower 70s...except at the beaches where clouds and
onshore winds will keep it cooler.
The overall pattern does not change much on Friday...but the high
pressure does weaken some...so the onshore flow will not be as
strong. Also...the winds may back a little...keeping the worst of
the clouds and showers offshore into the coastal waters.
Therefore...daytime temperatures could be a few degrees warmer due to less
clouds and weaker cool air advection. Overnight temperatures will drop to
On Saturday...a weak cold front essentially falls apart as it
approaches the area...allowing for a continuation of mainly dry and
sunny conditions with northeasterly winds and temperatures in the lower 70s
away from the coast.
Long term /Saturday night through Wednesday/...
reinforcing high pressure will build north of the County Warning Area on Sunday
and into early next week...maintaining the mostly dry
northeasterly flow. Temperatures will drop a few degrees will a modest
strengthening of low level cool advection...but should still be in
the middle 60s in the north to near 70 in the south...or fairly close
to normal. A stronger cold front will then approach from the west
for the middle of next week...introducing the best chance for
showers as the surface wedge finally gives way.
Aviation /20z Wednesday through Monday/...
both sites will be generally VFR through 18z Thursday. Some
numerical guidance indicates the potential for MVFR or lower
ceilings at ksav later tonight. The short-range ensembles are not
as impressed given fairly weak moisture return tonight. We hinted
at some lower clouds but maintained VFR at both sites.
Extended aviation outlook...VFR is expected to prevail.
a moderately pinched northeast gradient will persist through
tonight with Small Craft Advisory winds/seas all zones outside
Charleston Harbor. In The Harbor we expect 15-20 knots winds to
Thursday through Monday...small craft advisories will be needed for
the next several days due to a combination of winds and seas.
An extended fetch of northeasterly winds from the North Atlantic
into the coastal waters will cause seas to get up as high as 10 feet
in the offshore Georgia waters and as high as 7 feet in the
nearshore waters beyond 10 miles later this week. Winds will come
down slowly by Saturday...with seas following. Conditions will
gradually improve early next week.
current anomalies indicate tides should remain below advisory
levels this evening.
A coastal Flood Advisory has been issued for the Thursday morning
For Friday into the weekend...astronomical forcing and the surge
will be diminishing but coastal flood advisories may still be needed
each morning high tide into Saturday.
With the King tides and long fetch of the next couple of days...a
high surf advisory is also a possibility during the second half of
the week. Seas will build to as high as 4 to 7 feet in the nearshore
waters with decent breakers at the shoreline. Beach erosion in
vulnerable locations appears likely as well.
Georgia...coastal Flood Advisory from 6 am to 11 am EST Thursday for
SC...coastal Flood Advisory from 6 am to 11 am EST Thursday for
Marine...Small Craft Advisory until 6 PM EST Sunday for amz350-352-354.
Small Craft Advisory until 6 am EST Tuesday for amz374.