Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 251121
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
721 AM EDT Thu May 25 2017

.SYNOPSIS...
A cold front will push over the Atlantic this morning. High
pressure will build over the region today and will linger
through this weekend. A weak cold front is expected to slowly
slide over the region early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: The deep upper low over the Ohio Valley will track to the
east and begin to cross the central Appalachians. As it does, a
sharp trough axis and associated vorticity maximum will push
through the forecast area aloft. The surface cold front will be
solidly offshore by sunrise and the cyclonic flow around the
parent low to the north will drive a strong and gusty westerly
flow. The combination of the 3-4 mb pressure gradient and deep
mixing will help produce frequent wind gusts late this morning
and into the afternoon to around 30 mph. Conditions should
remain below wind advisory criteria, though motorists on area
bridges should be aware and take extra caution due to the
locally higher wind gusts. As the upper trough swings through,
it will bring with it an area of clouds and possibly even a few
showers thanks to the cooling aloft. The forecast continues to
carry slight chance PoP`s, mainly across the Tri-County region.
Temperatures will be below normal, with highs only reaching into
the upper 70s for most areas.

Tonight: Skies will clear out with the arrival of deep dry air.
Overall it will be a tranquil period with lows expected to fall
into the upper 50s for many inland locations.

Lake Winds: Gusty westerly winds are expected today across the
area. Winds directly over Lake Moultrie are expected to be in
the 15-20 knot range, with some gusts to around 25 knots for the
western shore line. Conditions should stay just below Lake Wind
Advisory criteria for the lake waters.

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY/...
Friday: Surface high pressure will overspread the region under
weak ridging aloft, continuing a period of calm weather with
almost zero probability for precipitation and mostly sunny skies
anticipated. Near-normal temperatures are anticipated with
highs reaching the lower to mid-80s before cooling into the mid
to upper 60s overnight away from the coast.

Saturday: Strengthening trough aloft to the west will induce an
area of low pressure at the surface over the central US. The
associated cold front will begin a slow trek southeast towards
the forecast area. High pressure at the surface will persist
locally under a ridge aloft, and another dry day looks highly
probable under this scenario. Temperatures climb back above
normal, aided by subsidence and some compression in advance of
the front. Expect high temperatures to reach the lower 90s away
from the coast and upper 80s at the beaches, with low
temperatures only dropping to around 70.

Sunday: The upper level ridge will slide east through the day,
leaving the forecast area on the western periphery as surface
high pressure continues. Subtle height falls aloft and ample
surface- based CAPEs would appear to support the development of
isolated thunderstorms later in the day. A fair bit of
uncertainty exists in model solutions, with the GFS ensemble
keeping the forecast area dry but the Canadian ensemble shows
generally light precipitation amounts for the second half of
Sunday. For now, the forecast will indicate a slight chance of
precipitation. Otherwise, anticipate high temperatures reaching
into the lower 90s most locations away from the beaches, with
low temperatures right around 70.

&&

.LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/...
The surface cold front will approach the area through the first
half of the week as the trough aloft slides east, bringing the
potential for another period of unsettled weather Monday through
Wednesday.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
VFR. Westerly winds will become quite gusty starting mid
morning and could gust to 30 knots at times. There could be an
isolated shower around KCHS in the early afternoon, but there
should be no impacts.

Extended Aviation Outlook: Expect VFR conditions to prevail.

&&

.MARINE...
Today: Very poor conditions are expected to prevail across the
local waters. The pressure gradient will tighten around a
surface low situated to the north. This will help drive a
persistent 20-25 knot westerly flow, with gusts to around 30
knots possible for all the waters at times. Small Craft
Advisories remain in effect. Seas will generally be 4-6 feet out
to 20 nm and 5-8 feet beyond.

Tonight: As the pressure gradient and low level jet subside,
winds will diminish through the night. Ongoing Small Craft
Advisories will come down, beginning in the evening, with all
flags down by midnight. Winds will remain elevated in the 15-20
knot range thereafter for most of the local waters. Seas will
subside as well, becoming 2-4 feet by sunrise Friday.

Friday through Monday: Conditions will gradually improve Friday into
Saturday under high pressure, with relatively tranquil conditions
persisting into Monday. Generally anticipate SW to WSW winds 10-15
kt with isolated gusts to 20 kt and seas 2 to 4 ft. Some shower
and/or thunderstorm activity will be possible later Sunday, with
chances increasing into the first half of next week as a cold front
approaches.

Rip Currents: Increasing astronomical influences and strong
westerly winds in the 20-25 knot range will combine to result in
a moderate risk of rip currents at all beaches.

&&

.TIDES/COASTAL FLOODING...
Blow out tides: Strong offshore westerly winds will occur at the
time of the early afternoon low tide to produce blow out tides.
In Charleston Harbor, low tide is expected to approach -2 feet
MLLW and at Fort Pulaski, low tide is expected to approach -2.5
feet MLLW.

Evening high tide levels will trend higher each day as we
approach the new moon and perigee this Friday, though we expect
tides to remain just below Coastal Flood Advisory stage.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 8 PM EDT this evening for AMZ330-
     352-354.
     Small Craft Advisory until midnight EDT tonight for AMZ350-374.

&&

$$

NEAR TERM...BSH
SHORT TERM...JMC
LONG TERM...JMC
AVIATION...BSH/JMC
MARINE...BSH/JMC
TIDES/COASTAL FLOODING...



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