Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 280801
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
401 AM EDT Wed Sep 28 2016

.SYNOPSIS...
A cold front will cross the area and stall along the coast late
Thursday. A reinforcing cold front will move through Friday night
and high pressure will fill in behind it for the weekend and early
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A pronounced closed upper low will drift slowly south through
Indiana and Ohio today while an associated surface cold front
pushes slightly closer to the forecast area from the SC Midlands.
Warm air advection will persist today though surface dewpoints
will generally be in the upper 60s to around 70. We expect
moderate surface-based instability to develop this afternoon with
1500-2000 J/kg and Lifted Indices of -4 to -5C. For much of the
day there will be little in the way of forcing for convective
development. The best chance for showers and tstms will be during
the latter half of the afternoon into the evening when the front
pushes closer to the area and upstream convection drifts east into
the area. A weak late afternoon sea breeze may also come into play
across the central portion of the area. We pared back pops during
the morning hours, then show increasing coverage across inland
areas during the afternoon. Scattered convection could persist
into tonight given the proximity of the front, though better
coverage should shift east into the adjacent Atlantic waters.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
Major guidance change in the last 24 hours is the weakening of the
upper cut-off low dipping down from the Great Lakes for the second
half of the week, and the less progressive solution taking the
feature no further eastward than the Ohio Valley. The result is
weaker cold air advection on the backside of the approaching surface
cold front, which will in turn weaken and slow the progression of
the front.

Despite our area now remaining in the warm sector of a broad surface
low working across the central Appalachians for much of the day
Thursday, the main band of low level moisture will shift off the
coast through the daytime hours, taking our highest precip chances
with it. Highest POPs will be kept midday for now, with decreasing
chances through the mid-to-late afternoon. The cold front should
enter the western portion of our CWA around sunset Thursday and
progress toward the coast through the evening. As the parent low
weakens the cold front will stall along the coast, keeping unsettled
weather in the forecast for the immediate South Carolina coast and
all coastal waters Thursday night.

The synoptic pattern Friday looks a bit nebulous as a broad surface
low slides over the Carolinas. A dry warm front looks to move
through the area during the day Friday, allowing warm air advection
to briefly fill in before a dry cold front moves through Friday
night, returning cold air advection to the area as high pressure
builds over the interior southeastern U.S. There does not look to be
enough moisture to justify POPs Friday or Friday night at this
point, but with such an unclear surface pattern confidence is
limited in how the models are handling the situation.

Saturday will see quiet weather with high pressure spreading over
the area while some semblance of a stationary front remains well off
the coast. The lowest temps of the period will be observed Saturday
morning with lows ranging from a couple degrees below normal along
the coast to 5 to 10 degrees below normal for inland areas.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
Upper level cutoff low over the Ohio Valley will lift back across
the Great Lakes and then get absorbed into the background westerlies
and carried across eastern Canada through the first part of next
week. High pressure over the Southeast will keep flow northeast to
onshore through the first half of next week, resulting in a mainly
dry forecast and temps a few degrees below normal for most of the
area through the period. The exception to the dry forecast is along
the coast, where a stationary front teetering offshore could bring
unsettled weather mainly in the afternoons.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
VFR. There is a risk for shallow ground fog at both terminal prior
to sunrise, but no impacts are expected at this time. Scattered
showers and tstms possible late this afternoon into the evening
but we still expect the best coverage farther inland so we
maintained dry TAFs at 06Z.

Extended Aviation Outlook: Brief flight restrictions in showers
and/or thunderstorms possible through midday Thursday. Mainly VFR
conditions expected thereafter.

&&

.MARINE...
South to southwest winds will continue through tonight with a
gradual increase in speeds due to nocturnal jetting. Seas will
respond slightly with 4 ft seas over outer portions by late
tonight.

Thursday through Sunday: Unsettled weather will persist
for the waters through at least Thursday night as a cold front
stalls out in the area. South winds as high as 15 to 20 kt ahead
of the front will give way to winds near or less than 10 kt when
the front moves over the waters. Northeast to east winds will fill
in for the weekend as high pressure builds inland. Expect seas
mainly 2-3 feet, with some 4 ft seas offshore Thursday.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$
NEAR TERM...JRL
SHORT TERM...CEB
LONG TERM...CEB
AVIATION...CEB/JRL
MARINE...CEB/JRL


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