Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 280537
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
137 AM EDT Sun May 28 2017

.SYNOPSIS...
High pressure will linger over the region through this weekend.
A weak cold front is expected to stall across the area early
next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Early this morning: No significant changes to the going
forecast. Regional radar imagery shows an ongoing line of
thunderstorms now pushing into the lee of the southern
Appalachians, with numerous reports of severe weather across the
western North Carolina mountains. The good news is that IR
satellite imagery shows a distinct warming trend for cloud tops
which is indicative of a weakening trend directly upstream of
the forecast area. A dry forecast continues through day break
though it will be interesting to see what role the residual
outflow boundary plays tomorrow during peak heating. Plentiful
debris mid/high level clouds will stream in from the northwest
overnight. It will be a mild night with lows only in the upper
60s in most areas.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY/...
Sunday: The mid/upper ridge will persist across the gulf coast
into southern GA, while a mainly zonal flow is noted across north GA
into SC. Late in the day, a series of weak short waves pass to the
northwest to north of the forecast area. Our low layered flow
remains westerly and this should pin the sea breeze closer to the
coast once again. Forecast soundings suggest a strongly capped
environment will exist and we continued to limit any slight chance
late day POP to north of a line from Allendale-Walterboro-Jamestown.
Thus with dry weather expected, it will be hot once again with
surface dew points elevating into the upper 60s to near 70. It will
be more humid with afternoon heat indices near 100 degrees in some
areas. Highs will reach the mid 90s Sunday afternoon and only fall
to the lower 70s many areas on Monday morning.

Monday: The upper ridge will shift over the Bahamas and there is
some subtle backing of the mid level flow across the region. There
is a noticeable mid-level cap through early afternoon, after which
it breaks. The best shortwave energy and deeper moisture will remain
west of the area during the day, though a weak cold front will push
into central GA/SC late. Highs will be in the mid 90s and dewpoints
around 70 many areas will yield fairly impressive CAPE values during
the afternoon. There will also be a fair amount of dry air aloft and
a good bit of instability between 700 MB and 500 MB. If the mid-
level cap does indeed break at some point on Monday, convection
should initiate pretty quickly. There is also the possibility that
some upstream activity will drift into the area. Convective indices
would support isolated severe thunderstorms, mainly across inland
areas late in the afternoon. Given the uncertainty regarding the
breakdown of the ridge we maintained pops no higher than 30%.

The cold front will stall near or over the area on Tuesday and upper
shortwave energy will move through north GA and the inland
Carolinas. Better coverage of mainly afternoon/evening showers and
thunderstorms is expected as mid level heights slightly lower during
the afternoon while 850 MB theta-e progs show good pooling. More
cloud cover will cut down on surface-based destabilization though
there will still be enough heating to push CAPEs above 1,000 J/kg,
perhaps above 2,000 J/kg along and east of I-95. Dry air aloft could
create a damaging wind potential with some of the storms.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A weak front will meander over the area mid to late week while
weak upper troughing will keep a steady stream of shortwaves
moving through. Decent coverage of showers and tstms expected
each day, mainly during the afternoon.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected to prevail through 06z Monday. One thing
to keep an eye on will be the slight chance of thunderstorms
near KCHS tomorrow. An outflow boundary from ongoing
thunderstorm activity could settle over the area during peak
heating tomorrow and serve as an initiating feature. Coverage
should be limited, if indeed there is any, so there is no
mention in the TAF at this time.

Extended Aviation Outlook: Mainly VFR conditions. Brief flight
restrictions possible in mainly afternoon/evening showers/tstms
starting Monday.

&&

.MARINE...
Tonight: High pressure will remain centered to the south while a
weak cold front approaches from the north. Winds will mainly be
south/southwest this evening before shifting to the southwest
throughout. Winds will be slightly elevated but no Advisories
are anticipated as any 25 kt gusts should be local and short-
lived. Seas will primarily be in the 1-3 ft range although will
get up to 4 ft closer to the Gulf Stream.

Sunday and Monday: High pressure centered over the southwest
Atlantic will maintain a southwest synoptic flow over the waters.
There will be diurnal surges in speeds, typical for the early warm
season pattern. Deeper mixing should favor a solid 15 KT flow with
gusts to 20 KT in the vicinity of the intracoastal Sunday afternoon
along the Charleston coast, otherwise 15 KT a typical flow for
Sunday afternoon and evening. On Monday, similar conditions but
the speeds will probably be a bit less given a weaker pressure
gradient in the boundary layer. Seas will average 3 FT or less.

Atlantic high pressure will generally prevail into mid week, though
a weaker gradient will ensue as a front stalls near the waters.
Southwest flow will prevail with modest afternoon sea breezes along
the coast.

&&

.TIDES/COASTAL FLOODING...
Tides will be running high through Sunday due to the new moon
and perigee. Fortunately the wind directions are not very
conducive for surge, but we could see very marginal coastal
flooding along the South Carolina coast during the evening high
tides Sunday.

&&

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

&&

$$

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


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