Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 221051
Area Forecast Discussion
National Weather Service Charleston SC
651 AM EDT Sat Oct 22 2016
Cool, high pressure will prevail through Sunday. A dry cold front
will move through late Monday and be followed by strong high
pressure into the middle of next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
No major changes were made for the late morning update.
Observations at PNOS1 indicate winds on Lake Moultrie have dropped
off considerably over the past 2 hours. The Lake Wind Advisory has
Dry high pressure will build into the region today. Strong cold
air advection will weaken through the day with the 850 hPa thermal
advection pattern becoming neutral to slightly positive this
afternoon in response to the cold pocket associated with the
departing upper trough propagating farther to the east. Chilly
mid-level temperatures will be counteracted somewhat by full
insolation and downslope dominated surface-700 hPa trajectories
from off the Southern Appalachians, but still expect a cool, fall-
like day. Highs will range from the upper 60s northern areas to
the lower 70s south of the I-16 corridor in Southeast Georgia.
.SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY/...
Tonight: Surface high pressure will build east tonight with the
center moving into western Georgia by sunrise Sunday. Should see
the boundary layer decouple by mid-evening across inland areas
while winds at the coast should stay in the 5-10 mph range for
much of the night. Low dewpoints, clear skies and light winds will
support a strong radiational cooling regime with temperatures
falling quickly after sunset. Lows will range from the lower 40s
inland to the lower-mid 50s at the beaches, in downtown Charleston
and around Lake Moultrie due to influences from the adjacent
warmer marine environment. Would not be surprised to some of the
normally colder, sheltered locations well inland drop into the
upper 30s briefly just before sunrise Sunday.
Sunday through Tuesday: Aloft, a long wave trough will remain
over the eastern portion of the country during the short term,
allowing NW winds to prevail across our area. At the surface, high
pressure across the deep south on Sunday will shift a little to
the west and weaken on Monday as a cold front approaches from the
north. There is very little moisture associated with this cold
front, so no rain is forecasted, just some high clouds. The front
will cross through the area Monday night followed by northern
plains high pressure building towards our region.
Temperatures will be the most noticeable weather element in the
short term. Despite abundant sunshine and some downslope flow off
the mountains on Sunday, temperatures will only top out in the lower
to mid 70s, mainly because the air mass starts out very cool in the
morning. Sunday night lows should be in the mid 40s far inland,
moderating to the 50s along the immediate coast. Monday will be the
warmest day of the short term, with compressional heating in advance
of the cold front boosting temperatures back above normal, in the
upper 70s to lower 80s. Monday night low temperatures will also be
warmer, the lower 50s far inland, moderating to the 60s along the
immediate coast. There is not too much cold air advection forecasted
behind the cold front on Tuesday. Plenty of sunshine and thickness
values support high temperatures in the lower to mid 70s, and the
upper 70s near the Altamaha.
.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
High pressure to our north is forecasted to build towards our area
by Wednesday, bringing dry conditions and seasonal temperatures. As
the high shifts offshore Thursday the models have differing outcomes
for the forecast. The 00Z ECMWF brings a surface low through the
Great Lakes region and an associated cold front stretching into
south. The front crosses through our area Thursday night into
Friday, bringing some showers. Meanwhile, the 00Z GFS takes the same
low, links it up with an upper level low that it develops and takes
both of these features into the deep south where they weaken by
Friday. This outcome will give us some showers. Went with slight
chance showers for now, but this will need to be refined as future
model runs come into better agreement.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
Extended Aviation Outlook: VFR.
Today: An ASCAT-B pass just before 05z showed winds were a solid
30 kt over parts of the Georgia offshore waters with the core of
the strongest winds remaining just south of buoy 41004. Given
deep mixing profiles that were in place within a strong cold air
advection regime, frequent gusts to gale force likely occurred for
about a 2-3 hour period between 03-06z. Winds will continue to
diminish today as the terminal advection pattern becomes neutral
and high pressure builds in from the west. Both winds and seas
will remain high enough to keep Small Craft Advisories in place
for the nearshore waters and Charleston Harbor this morning and
into the early afternoon hours for the Georgia offshore leg. Seas
4-6 ft nearshore...6-8 ft offshore will subside to 1-3 ft
nearshore....3-5 ft offshore this afternoon.
Tonight: A slight evening surge will occur over the waters as
inland areas cool with winds staying a bit elevated due to an
enhanced inland/water thermal gradient. Speeds could get as high
as 15-20 kt for a period this evening before settling back down
to around 15 kt. Seas will average 1-2 ft nearshore waters with
2-4 ft offshore waters.
Sunday through Wednesday: High pressure across the deep south on
Sunday will shift a little to the west and weaken on Monday as a
cold front approaches from the north. The front will cross through
the region Monday night followed by northern plains high pressure
building into the area by Wednesday. An increased pressure gradient
between these two features will lead to increased winds and seas.
Small Craft Advisories may be needed midweek.
MARINE...Small Craft Advisory until 11 AM EDT this morning for AMZ350-
Small Craft Advisory until 2 PM EDT this afternoon for AMZ374.