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Area Forecast Discussion

516
FXUS62 KCHS 221752
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
152 PM EDT FRI JUL 22 2016

.SYNOPSIS...
High pressure will gradually shift offshore and persist through
much of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this afternoon: No change to the forecast thinking. Minor
updates to hourly grids. Previous discussion follows below.

Late this morning: Land areas have remained dry while scattered
showers/thunderstorms have the coastal waters have spawned a few
reports of waterspouts off the Beaufort County coast. This
activity is diminishing and focus for the rest of the day will
turn inland. Aloft, water vapor imagery shows the region being on
the far eastern extent of the large ridge and associated
anticyclone centered over the plains and the lee of the Rockies.
The prevailing flow aloft is north to northeast and a large area
of NVA is covering much of the southeast coast. There is some very
weak shortwave energy upstream, but nothing that looks overly
significant. The weak surface pressure pattern will prevail and
feature a mainly light onshore southerly flow. The main question
for the day concerns convective coverage. Modifying the 12z KCHS
RAOB shows the potential for around 2000 J/kg of CAPE with typical
mid level lapse rates and 500 mb temperatures for this time of
year. There is plentiful dry air, and DCAPE values could be as
high as 1500 J/kg this afternoon. Hi-res models are very
unimpressive and mainly show isolated weak activity along the sea
breeze this afternoon. Given that there doesn`t appear to be a
strong cap or anything to prevent convection all together, have
expanded the slight chance POP to include the entire coast.
Coverage will not be high but given the high DCAPE values and
large separation between the freezing level and the wet bulb zero
height, it`s not out of the question to see a strong to marginally
severe storm. Damaging winds would be the main impact to watch
for. Otherwise, expect highs in the low to mid 90s with heat
indices 100-105 at times.

Tonight: Any lingering showers or thunderstorms will diminish
early with dry conditions overnight. Temps should bottom out in
the lower to mid 70s inland and near 80 at the coast.

&&

.SHORT TERM /SATURDAY THROUGH MONDAY/...
The surface pattern will remain fairly stagnant through the
period, with the primary features being Atlantic high pressure and
a trough of low pressure situated inland. Aloft, upper ridging
will weaken late Saturday into Sunday as a cutoff low and
associated vort max shifts west across far southeast Georgia and
the Florida Panhandle. On Monday, the ridge will briefly rebuild
before shortwave energy moves into the Great Lakes region.

Precipitation chances will largely be diurnally driven, primarily
originating from the sea breeze or convergence along the piedmont
trough. Organized severe threat looks low given weak deep layered
shear, however isolated severe storms are possible especially where
boundary interactions occur.

High temperatures forecast to be a couple degrees above normal,
mainly in the mid to upper 90s away from the immediate coast. Heat
indices forecast to stay below the local heat advisory criteria of
110, peaking around 105-107. Lows in the mid/upper 70s.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
The forecast area will remain on the western periphery of Atlantic
high pressure while a piedmont trough sits inland. A weak front will
approach from the northwest mid week but will likely stall and
eventually dissipate before reaching the local area. Fairly typical
summertime PoP scheme, with shower and thunderstorm coverage peaking
in the afternoon/evening when instability is greatest. Temperatures
forecast to be at or a couple degrees above normal through the
period.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
VFR conditions are expected to prevail at KCHS and KSAV through
18z Saturday. There is still a very low chance for a thunderstorm
to impact the terminals this afternoon, but chances are too low to
include in the forecast. The better chance would be at KSAV, but
even there the likelihood is too low. There could be some patchy
fog across the region late tonight, but it is expected to remain
well inland of the TAF sites.

Extended Aviation Outlook: Brief flight restrictions possible with
afternoon showers/thunderstorms. Otherwise, VFR conditions expected.

&&

.MARINE...
Today and Tonight: A weak pressure gradient expected to prevail
with high pressure in control. Variable winds will become
south/southeast today and then south/southwest tonight, possibly
increasing a tad due to nocturnal surging, although remaining 15
knots or less. Seas will mainly range from 2-3 feet, highest
toward the Gulf Stream, but up to 4 feet well off the GA coast
this morning. Conditions appear favorable again this morning for
waterspouts associated with any cumulus cloud lines that develop.

Saturday through Wednesday: Atlantic high pressure will prevail
through the period while a piedmont trough persists inland.
South/southwest winds will generally be 15 knots or less, peaking in
the afternoon with the sea breeze circulation and then again at
night over nearshore Atlantic waters due to nocturnal jetting. Seas
2-3 feet on average.

&&

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

&&

$$

NEAR TERM...BSH/RJB
SHORT TERM...ECT
LONG TERM...ECT
AVIATION...BSH/ECT
MARINE...ECT/RJB



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