Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 200210
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
1010 PM EDT Thu Apr 19 2018

.SYNOPSIS...
Cool and dry high pressure will build in behind a dry cold
front tonight through Saturday night. Unsettled weather is
expected late Sunday through at least Tuesday as low pressure
moves up the coast.

&&

.NEAR TERM /THROUGH FRIDAY/...
The post-frontal wind shift to north can be seen advancing
south through the Charleston Tri-County area this evening. Much
cooler air will continue as advance south and east over the
region overnight as high pressure builds from the Northwest.
Our forecast needed only subtle initialization adjustments to
temps and winds this evening and remains on track with clear
skies overnight, veering surface flow to northeast by daybreak
with some noticeable gusts at times as the cooler air mass
arrives. We maintained lows in the mid 40s north to lower 50s
southeast zones of GA.

Lake Winds: Steepening low level lapse rates overnight coupled
with 30-35 kt of cooler north flow between 1000 and 1500 ft
suggest a decent period of gusty winds overnight, especially
across open lake waters of Moultrie. We issued a Lake Wind
Advisory which is values until mid-late morning on Friday.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Cool and dry high pressure will build in from the northwest
Friday, then shift offshore during the day Saturday. Clear skies
will prevail Friday and Friday night, then some cumulus will
develop across southeast GA on Saturday as the flow turns
onshore. High temps will be in the upper 60s to low 70s Friday
and low to mid 70s Saturday. Saturday morning lows in the 40s
will be rather chilly for late April.

A deep cutoff low will move toward the Arklatex region on
Sunday while weak ridging persists over the local area.
Isentropic ascent ahead of the upper low will at a minimum
spread increasing clouds over the area, along with the potential
for scattered showers, mainly in southeast GA. We maintained
similar PoP schemes on Sunday with far northern areas dry
through the day with increasing PoPs as one moves to the south.
In-situ dry air to the north should limit the ability for
precipitation to spread north during the daytime. Highs will be
in the upper 60s to low 70s.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A blocking pattern develops aloft, with a deep cut-off spiraling
over the Tennessee valley early in the week, while an amplified
ridge is situated near or off the eastern seaboard. Strong surface
high pressure to the north, and the approach of the surface low from
along the northern Gulf coast will provide an excellent set up of
overrunning rains. The low is presently expected to track near or
just south of the region Monday, then over or just east of the
region Tuesday. Large scale lift and upper difluence, the slow
progression of the low both surface and aloft, plus PWat as high as
near the 90th percentile will bring us some much needed rainfall.
Depending upon the exact track of the low there is some potential
for t-storms, especially south and east. By mid week the cut-off low
opens up and is kicked out to the east as a strong short wave drops
through the upper Midwest. This will eventually allow for drying to
occur late in the forecast cycle. Breezy to windy weather will
prevail early in the week with a tight gradient between the low and
high pressure to the north.

&&

.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
VFR. Gusty winds will continue at times for both KCHS and KSAV
through the overnight period in the wake of a dry cold front.

Extended Aviation Outlook: VFR weather will persist into early
Sunday, before flight restrictions become likely later Sunday
through Tuesday as low pressure impacts the area with rain and
breezy conditions.

&&

.MARINE...
Tonight: The flow will shift to north overnight in the wake
of cold front and increase overnight as high pressure builds
into the region behind a cold front. At 02Z upstream surface
pressure rises were near 2 MB an hour and significant surging
is likely as cold air advection takes hold and near-water lapse
rates steepen. A tightening pressure gradient will support north
to northeast winds 20-25 kt with seas building 4-6 ft nearshore
waters and 6-7 ft offshore waters. For the Charleston Harbor,
winds will be north 15-20 kt with gusts to 25 kt, but could be
locally higher near the Harbor entrance. Small Craft Advisories
are in effect for all waters overnight.

Friday through Tuesday: Ongoing Small Craft Advisories will
gradually drop off for the nearshore waters on Friday as cold
advection wanes and the northeast gradient relaxes. An SCA will
continue for the offshore GA waters until Saturday evening,
mainly due to some lingering 6 ft seas over outer portions.

The surface high moves off New England and gives way to low
pressure that impacts the area early next week with elevated
chances for rain and some stronger t-storms. The worst conditions
look to be early next week, with poor to potentially dangerous
marine weather to occur.

Rip Currents: A prolonged stretch of moderate to perhaps strong
onshore winds and larger surf, as low pressure passes nearby early
next week, will lead to an enhanced risk of rip currents at the
beaches.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until 11 AM EDT Friday for SCZ045.
MARINE...Small Craft Advisory until 2 PM EDT Friday for AMZ352.
     Small Craft Advisory until 11 AM EDT Friday for AMZ330-350.
     Small Craft Advisory until 5 PM EDT Friday for AMZ354.
     Small Craft Advisory until midnight EDT Saturday night for
     AMZ374.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...



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