Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 250800

Area Forecast Discussion
National Weather Service Charleston SC
400 AM EDT WED MAY 25 2016

Atlantic high pressure will prevail through Friday. A wave of low
pressure is then expected to develop over the western Atlantic and
approach the southeast coast as early as this weekend. The forecast
then becomes quite uncertain and the low could meander off the
southeast coast into early next week.


Pre-dawn: A few mid and high level clouds lingered overnight but
most areas should see mainly clear skies as daybreak approaches.
temps were running milder than 24 hours ago thanks to the surface
ridge axis now offshore lending to elevated low level dew points.

Today: Deep layered ridging along with dry air and subsidence aloft
providing a dry weather regime across the forecast area. Increased
upper heights and low level thickness values suggest a continuation
of warmer temps for the region. Readings should quickly warm to
near yesterday`s highs by early afternoon with max readings today
reaching the upper 80s in many areas inland from the beaches and
barrier islands. There should be some cumulus fields developing
with the sea breeze this afternoon along with a few high clouds at

Tonight: Quiet conditions will persist with mainly clear skies and
light to near calm winds. Low temps will range in the lower 60s
inland to the upper 60s right along the coast.


Thursday and Thursday night: Large scale ridging aloft will prevail
across the eastern CONUS as high pressure at the surface will remain
in control for the forecast area. Plentiful dry air in the mid and
upper levels combined with a prominent subsidence inversion noted in
model soundings will keep the forecast dry through the day and the
overnight. The pattern will support temperatures that are summerlike
with highs in the upper 80s and lows only in the mid 60s.

Friday through Saturday: Forecast complexity begins to increase into
the start of the weekend. The models have been rather consistent for
a few days now with developing a wave of low pressure over the
western Atlantic early Friday and tracking it westward through
Saturday. In fact, the models are in excellent agreement on the
placement, strength, and track of the low from Friday morning through
Saturday morning. Any deep moisture associated with this system (be
it tropical, subtropical, or otherwise) looks to stay offshore
through Saturday morning, with just showers perhaps brushing the
coast late Friday night. Then during the day Saturday, the ECWMF and
GFS both only allow the low to make minimal progress toward the
coast and keep it centered some 150-200 miles to the southeast of
the mouth of the Savannah river. It is at this point that the
uncertainties surrounding the system begin to increase exponentially.
The classification of the system as it sits over the Gulf Stream
will be in question, as will the western extent of any deeper
moisture surrounding the system and its inland penetration into
the forecast area. As a result, forecast confidence is quite low.
For now, we feature slight chance to chance pops with a west to
east gradient, accounting for pockets of improved moisture pushing
in from the east. Temperatures are pegged in the mid to upper 80s,
but this will also be dependent on the low and its attributes.


Forecast confidence is quite low for the long term period and the
details of the forecast hinge significantly on the status, strength,
and eventual track of an area of low pressure expected to be sitting
off the southeast coast starting Saturday night. Attempting to nail
down specifics in such an uncertain forecast at this point would be
an exercise in futility. Instead we will have to wait and see how
the large scale environment unfolds and what impacts the wave of low
pressure will have on the forecast area. Overall, the system appears
as though it will be an environment with very weak steering flow
which would seem to favor a system that could meander about with
little forward progress. Another thing to keep in mind is that the
system is progged to be sitting over the Gulf Stream, possibly into
early next week. Within a weak steering flow environment it may be
difficult to envision the system moving off the Gulf Stream and may
favor a slow offshore track. Much is yet to be determined and the
forecast will be refined a model consensus develops.


VFR through 06Z Thu. Very low probability for ground fog around
daybreak this morning.

Extended Aviation Outlook: Primarily VFR.


The surface ridge axis will be aligned sw-ne off the Georgia and
South Carolina coasts through tonight. This will maintain a se-s
synoptic flow with speeds mainly averaging 10 kt or less through
tonight and seas 1 to 3 ft, highest well offshore.

Thursday through Sunday: High pressure over the Atlantic will
prevail into Friday when a developing wave of low pressure is
expected to track eastward toward the southeast coast. The forecast
is then quite uncertain for the weekend and will ultimately be
determined by the location, strength, and track of the wave of low
pressure. As it stands for now, the forecast features a rather
modest northeast flow with speeds generally no more than 15 knots.
Seas top out in the 2-4 ft range with some 5 ft seas possible in the
outer waters this weekend as the northeast fetch increases.

Rip Currents: There could be increased risk of rip currents at area
beaches over the holiday weekend as an onshore flow strengthens a
bit ahead of a tropical wave coincident with a slight uptick in
swell energy.




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