Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 271956
Area Forecast Discussion
National Weather Service Charleston SC
356 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/...
A cold front will stretch across the Appalachians this evening.
Radar imagery shows a line of showers and thunderstorms moving
across central GA, tapping into the moisture and instability
ahead of the front. The major computer models show BLCAPES
approaching 1,500 J/kg reaching the far western portions of our
area ahead of this line early this evening. However, these
models along with the CAMs show this convection dissipating as
it reaches our far western portions, due to the stabilizing
atmosphere with the setting sun. To account for this, we have a
chance of thunderstorms for some of our far inland counties
early this evening. It`s not out of the question that a strong
storm could tap into the DCAPEs exceeding 1,000 J/kg and
generate some stronger winds. Regardless, this inland convection
is expected to dissipate later this evening. Also ahead of the
front, low level southerly winds will remain steady and the
pressure gradient across the area should increase dewpoints to
the upper 60s to around 70 degrees. Weak isentropic flow and
increasing low level moisture should yield an increasing deck of
low stratus, especially over the inland zones. In addition,
weak instability and low LCLs may allow showers and storms to
develop over the marine zones and portions of the Tri County
late tonight. Low temperatures may only reach around 70 degrees.
.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 /20Z THURSDAY THROUGH TUESDAY/...
Mainly VFR. Gusty southerly winds will gradually ease this
evening. The combination of some lift from an approaching cold front
to our west and increasing low level moisture should yield low
stratus tonight. MVFR ceilings are possible. However, confidence
was not high enough to include this in the current TAFs.
Regardless, the stratus is expected to dissipate in the
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 this evening
and overnight. The pressure gradient should equate to southerly
winds increasing to 15-20 kt across most of the coastal waters
this evening, then easing a bit after midnight. As a result, wave
heights should build to 4-5 ft this evening before subsiding
about a foot after midnight. Some 6 footers are possible beyond
20 nm, but confidence was not high enough to issue a Small
Craft Advisory for AMZ374.
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 the upcoming Perigean Spring Tide will
generate a Moderate Risk of Rip Currents along southeast South
Carolina beaches through Friday, with a low risk for our
Coastal Flood Advisories are in effect this evening.
Elevated tides are expected to continue through Saturday, so
more advisories will likely be needed with each evening high
GA...Coastal Flood Advisory from 8 PM to 11 PM EDT this evening for
SC...Coastal Flood Advisory from 8 PM to 11 PM EDT this evening for