Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 182353
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
753 PM EDT Sat Aug 18 2018

.SYNOPSIS...
The area will be situated between an inland trough and Atlantic
high pressure through the first part of next week. A cold front
will approach the area from the west towards the middle of next
week, then stall over or near the region through the end of the
week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Active convection ongoing across southeast SC nearing dusk.
Multicell tstms with some occasional potential for localized
damaging wind gusts moving through the Charleston Quad-county
area with most of the stronger storms inland from U.S. 17.
Elsewhere, bands of convective debris showers producing lighter
showers extended across the forecast area. Coverage of showers
and storms should continue to dwindle later this evening per
latest high resolution models. Lows will range from the lower
to mid 70s inland to closer to 80 near the coast.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday: A dampening short wave will be moving through the NE part of
the nation, followed by another short wave dropping through the
western Great Lakes during the daylight hours, then into the OH
Valley during Sunday night. As this transpires the sub-tropical
ridge, both surface and aloft is able to build a tad further across
the local area. The atmosphere remains capped during Sunday morning,
but with moisture to continue above normal, and instability about
average for the latter part of summer, we do anticipate convection
to form on the sea breeze and to advance into the area from the W-SW
in the afternoon. We have slight chance PoP near the coast, with 30-
50% PoP inland, greatest near and inland from I-95. The chances for
convection could get a boost from a weak short wave near the
northern Gulf Coast tonight, that moves across our NW tier late in
the day and early at night, and divergence associated with the nose
of an upper jet streak. These features could allow for a little
better chance of cold-pooling from about 22Z-04Z, and maybe some
risk for loosely organized convection to occur. DCAPE is as great as
800-1000 J/kg, suggesting that a few storms could produce strong or
marginally severe downbursts of wind. There is enough flow to negate
any significant flooding concerns, but given the abundance of
moisture, a few storms will produce heavy downpours with localized
flooding to occur. Persistence is the best forecast regarding both
max and min temps.

Monday and Tuesday: A short wave will pass through the mid-Atlantic
region late Monday, with a stronger short wave trough situated in
the central U.S. on Monday to begin dampening as it passes through
the western Great Lakes and OH/TN Valleys on Tuesday. Our area is
influenced more by sub-tropical ridging from the Atlantic along with
a little higher mid level heights and associated subsidence. There
is still enough instability and moisture to generate our typical
diurnally driven convection. But since the main triggers will be the
sea breeze, the inland trough and the usual meso-scale boundaries,
we are showing no more than isolated to scattered PoP through the
period. Despite this, given more dry air in the H7-H4 layer, DCAPE
is greater and could lead to a better chance of a few pulse type
severe storms. Temps will average above normal, both during the day
and at night.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Models are in fairly good agreement showing a long wave trough over
the eastern half of the country Tuesday night. This trough will
gradually shift eastward and then lift to the north into Friday. At
the surface, a front is forecasted to stall over or nearby our area
during this time period. This will lead to above normal POPs and
near or maybe even below normal temperatures. But if the front
positions itself further offshore, then large changes in the
forecast would be needed.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
KCHS: VCTS through late evening with chances for tstms to
directly impact the airport but radar trends have complex on
the ocean-side of the sea breeze. VFR otherwise overnight
through 18Z. Late day tstms are again possible Sunday afternoon.

KSAV: VFR tonight as convection was moving away from the north
this evening and a few light showers from convective debris
through late evening. Convection possible on Sunday afternoon
as the pattern is similar to today.

Extended Aviation Outlook: Only a small potential for flight
restrictions in mainly diurnal convection through Tuesday at KCHS
and KSAV. A better chance of flight restrictions in SHRA/TSRA on
Wednesday with an approaching cold front.

&&

.MARINE...
Tonight: Southerly flow regime will hold in place, similar to
the past several days. South/southwest winds will peak around 15
kt, with some winds near 20 kt at times. Seas will average 2-4
ft, highest near the Gulf Stream.

Sunday through Tuesday: There remains a decent gradient between a
lee side trough and the sub-tropical Atlantic ridge to the S-SE.
With a boots from sea breeze circulations and subtle nocturnal low
level jetting, S-SW winds will peak as high as 15 or 15-20 kt, with
occasional stronger gusts. But certainly not frequent or high enough
for any Small Craft Advisory headlines. Seas will reach nothing
more than 3 or 4 ft. Isolated to scattered showers and t-storms
will occur, mainly during the mornings and at night.

Wednesday and Thursday: A weakening cold front will approach the SE
coast during this time, stalling near the local waters late in the
period. Winds and seas will remain below any advisory thresholds,
but the potential for showers and t-storms will increase due to the
proximity of the front.

&&

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

&&

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


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