Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 282309
Area Forecast Discussion
National Weather Service Charleston SC
709 PM EDT Fri Apr 28 2017
Early summer conditions will prevail over the weekend as strong
high pressure holds offshore. A cold front will cross the coast
early Tuesday bringing a chance of showers. A Gulf low pressure
system may bring a soaking rain late next into the early part
of next weekend.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A building ridge aloft and strengthening high pressure at the
surface and lower levels will encompass the area through the
night. A warm night for late April is expected with decent
mixing in the boundary layer, so no lower than the upper 60s
well inland and low to middle 70s along the coast to occur.
Low stratus that is already along parts of he SC coast and
patchy sea fog moving onshore has prompted us to include patchy
fog along the coastal corridor, where the lowest condensation
pressure deficits will occur. Further inland it will be mainly
stratus given geostrophic winds of 15-20 kt.
Smoke from the West Mims wildfire in the Okefenokee Swamp has
been spreading north toward tattnall and Long counties, but
there have been no signs of any reductions in surface
visibility, so far. Still, parts of SE GA could experience a
smell of smoke in the air tonight within the southerly flow.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
As of 3 PM Friday: Highly amplified pattern creates hot
temperatures through the weekend ahead of a cold front which
will cross offshore Monday night.
590+ dm ridge will be centered just offshore Saturday before slowly
migrating eastward on Sunday. This ridging combined with surface
Bermuda-type high pressure will push 850mb temps up to 14-16C, which
combined with abundant sunshine thanks to exceedingly dry air aloft
will drive highs into the low 90s inland on Saturday, mid 80s at the
coast, but still only around 80 at the beaches due to a strong and
early-developed sea breeze. Temps on Sunday will be only a degree or
two cooler as the thermal ridge weakens slightly. While isolated sea
breeze showers are possible each aftn, the very dry air aloft will
cap potential, and will continue inherited silent POP Saturday, SCHC
on Sunday. As the cold front begins to encroach on the area late
Sunday, and especially on Monday, southerly winds will crank up as
well, keeping minimums well above seasonable norms, falling only to
a degree or two either side of 70 both Saturday and Sunday nights.
The cold front Monday will race east as a bowling ball upper low
rotates into the Great Lakes pushing the cold front off the coast by
Tuesday morning. Timing of FROPA is expected to be late Monday
night, but strong shear and moderate instability ahead of it will
create a good chance for tstms Monday aftn and Monday night.
Increased cloud cover and lowering heights will keep highs and lows
on Monday several degrees cooler than during the weekend.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A weakening cold front looks to push offshore Monday night followed
by generally drier/cooler weather through Wednesday before rain
chances return with the approach of another storm system. At this
point there is uncertainty regarding this system so forecast
confidence is lower than normal, especially later in the week.
Temperatures should be near or above normal, but could drop below
normal Friday if the storm departs by then.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
KCHS: Areas of pre-existing low clouds near the terminal could
spread into or develop over the airfield overnight, leading to
MVFR or potentially IFR conditions from 07z-14Z Saturday.
However, flight restrictions are certainly possible prior to
this time, similar to last night. Otherwise, VFR weather will
prevail. Gusty S winds will be common Saturday afternoon with
deep mixing and sea breeze circulations to occur during the
warmest part of the day.
KSAV: VFR conditions will prevail much of tonight and Saturday.
outside the exception of about 4-5 hours of MVFR or possible IFR
weather in low stratus a few hours either side of daybreak
Saturday. Gusty S-SE winds to occur Saturday afternoon due to
the sea breeze, deep mixing and peak heating.
EXTENDED AVIATION OUTLOOK: Restrictions due to low ceilings will be
possible at either terminal Saturday night, possibly persisting
into early the following morning. Ceiling and/or vsby restrictions
will again be possible Monday into early Monday night due to
showers and/or thunderstorms. Also...breezy/gusty conditions
S winds 10-15 KT generally across the waters with seas mainly
in a 3-4 foot range shared by weak SSE longer period swell and a
moderate S chop in 4-5 seconds wave periods. A few inshore gusts
will exceeded 15 KT through early evening due to the sea breeze
circulation near the coast. Webcam and satellite imagery
indicate the threat of dense sea fog is retreating, and the
Dense Fog Advisory has been canceled. However, patchy fog
remains in the forecast, first over the SC nearshore waters,
then expanding further south overnight. The fog could move into
the Charleston Harbor at times, and we will maintain a close
weather watch for possible dense fog.
Saturday through Wednesday: High pressure offshore will be the
dominant feature through the weekend before a cold front
approaches the waters late Monday. Between these two features,
southerly winds will gradually increase during the weekend,
rising from 10-15 kts Saturday, to 15-20 kts by late Sunday. As
the cold front approaches during Monday, winds will veer more to
the SW and increase further to 20-25 kts, and an SCA will
likely be needed as seas build from 2- 4 ft Saturday, to as high
as 5-7 ft on Monday, with some 8 ft seas possible in the outer
portion of the GA waters. For Charleston Harbor, winds are
forecast to also go above SCA thresholds, primarily late Monday
immediately ahead of the FROPA.
As coastal flood advisory is effective to coincide with the
elevated astronomical tide tonight for both the GA and SC
coastal zones. The peak of flooding should reach slightly higher
levels than last night generally at maximum between 1030PM and
11PM most locations.
GA...Coastal Flood Advisory until midnight EDT tonight for GAZ117-
SC...Coastal Flood Advisory until midnight EDT tonight for