Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 280247
Area Forecast Discussion
National Weather Service Charleston SC
1047 PM EDT Thu Apr 27 2017
A weak disturbance is expected to affect the area tonight, followed
by high pressure Friday into the weekend. A cold front will move
through Monday night, then a stronger storm system will affect
the area mid to late week.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Scattered convection off to the W-NW of the area should
generally remain outside the CWFA within the Sw to Ne steering
flow. But we have indicated isolated PoP across the immediate
NW tier through midnight just in case meso-scale boundary
interactions spur a shower or t-storm. Overnight we do find
isentropic ascent and low level coastal convergence, maybe
enough to generate a few showers or t-storms brushing Charleston
County, but nil PoP`s elsewhere.
Turbulent mixing within the boundary layer will negate the need
for any mention of fog, although there is considerable moisture
beneath a well pronounced nocturnal inversion, which will lead
to a deck of stratus. Already we`re seeing indications of that
at a few sites (KSSI and KGGE), and more locations will start
reporting it overnight as condensation pressure deficits lower
to less than 20 or 30 mb.
It will certainly be a a warm night by April standards within a
southerly synoptic flow combined with the low stratus and/or
convective debris clouds. This will prevent temps from dropping
any lower than the mid or upper 60s, which is about 10-12F
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
The Bermuda High will continue to expand into the forecast area
through Sunday, with onshore flow around the High maintaining low-
level moisture. This will promote a primarily rain-free but humid
pattern over the weekend. Prognosed moisture convergence near the
coast under varying levels of capping suggests a nonzero probability
for an isolated shower or two to develop dependent on the strength
of the seabreeze, but occurrence appears unlikely at this time with
the most probable outcome being a diurnal cumulus field. Under this
regime, temperatures will remain several degrees above normals, with
maximum temperatures reaching the upper 80s and lower 90s away from
the coast with minimum temperatures only in the lower 70s or upper
60s. Some uncertainty is introduced Sunday as high level clouds
ahead of a developing low pressure system appear poised to move over
the forecast area, but some model soundings indicate potential for
low-level stratus-type development early Sunday morning. Prevalent
cirrus cover would assist in mitigating this occurrence. While the
net effect on sky cover is moot, this would serve to keep maximum
temperatures a degree or two cooler than previous days.
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
A mature surface cyclone will lift northeast into the Great
Lakes region Sunday night and Monday, pushing a cold front
through the local area Monday night. A decent channel of
atmospheric moisture ahead of the front will allow scattered to
numerous showers and thunderstorms to move through Monday
afternoon and Monday night. A deeper upper trough moving through
the central United States late week will bring a stronger low
pressure system through the area, accompanied by numerous
showers and tstms.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Mainly VFR, although there are indications of flight
restrictions for a few hours late tonight into Friday morning
due to a low stratus deck. South winds will increase again
Friday afternoon due to max heating and enhancement from the sea
Extended Aviation Outlook: Flight restrictions due to low ceilings
will be possible at either terminal Friday and Saturday nights,
possibly persisting into early the following morning. Ceiling and/or
vsby restrictions will again be possible Monday into Monday night
due to scattered showers and/or thunderstorms.
A cold front will stretch across the Appalachians overnight.
The pressure gradient between this front and Atlantic high
pressure will equate to southerly winds increasing to 15-20 kt
across most of the coastal waters, then easing a bit late. As a
result, wave heights will average 3-5 ft.
Generally onshore flow averaging 10-15 kts will persist through the
weekend, though winds nearest the coast may veer southwest or even
west-southwest each night as a land breeze develops after sunset.
Seas will generally remain 2-4 feet through the period. A cold front
will approach the region Sunday into Monday, and flow will increase
in advance of its arrival, building some 5-6 feet seas offshore as
early as Sunday, with Small Craft Advisory conditions arriving over
most of the waters Sunday night, persisting into Monday night.
Rip Currents...The combination of swell impacting the beaches, an
afternoon sea breeze, and astronomical influences will generate
a Moderate Risk of Rip Currents along southeast South Carolina
beaches Friday, with a low risk for our Georgia beaches.
Elevated tides are expected to continue through Saturday, so
more advisories will likely be needed with each evening high