Area Forecast Discussion
Issued by NWS Charleston, SC
FXUS62 KCHS 212320
Area Forecast Discussion
National Weather Service Charleston SC
720 PM EDT Fri Oct 21 2016
Cool high pressure will prevail this weekend. A dry cold front will
move through late Monday, followed by strong high pressure into the
middle of next week.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
A strong cold front had pushed offshore and will lead to breezy
conditions through this evening due to post-frontal cold air advection
and pressure rises. A Lake Wind Advisory is in effect for Lake
Moultrie for gusts near 30 knots /35 mph/ where low-level mixing
will be enhanced given the warm lake waters. Otherwise, winds will
diminish after midnight but remain elevated. Lows will range from
the mid/upper 40s inland to the mid 50s at the beaches.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH MONDAY/...
Big changes this period featuring much cooler conditions, although
our noticeable lack of rainfall will continue.
High pressure extending from the upper Midwest to the northwest Gulf
on Saturday pushes east to a position directly overhead Sunday, then
gives way to a cold front from the north that approaches Monday. The
mean long wave trough aloft will remain over the eastern portion of
the nation into early next week, with a deep NW flow to prevail
across the local area.
The atmospheric column is void of any moisture this weekend, with no
more than a little jet induced cirrus clouds Monday. Suffice to say
abundant sunshine will be the rule, and that along with downslope
flow off the mountains will negate some of effects of the noticeably
cooler air mass. We`ll stay close to thickness forecast Saturday and
Sunday, which supports only upper 60s and lower 70s Saturday, with
moderating conditions Sunday allowing for max temps mainly in the
lower and middle 70s. Monday will be the warmest of the short term,
with compressional heating in advance of the cold front to boost
temps back above normal in the upper 70s and lower 80s.
Meanwhile, Saturday Night promises to be the coldest we have seen
since last March. Not anywhere near record lows, but with dew points
in the 30s and 40s, clear skies and little to no wind, temps will
easily fall to 40-45F inland from US-17, upper 40s or lower 50s
along the coast and in downtown Charleston. A few pockets of upper
30s are possible in Allendale, northern Berkeley County, and maybe
west of US-301 in Georgia, but frost seems unlikely. Sunday Night
will again be cool, but a modifying air mass and warmer conditions
during the daylight hours won`t allow for it to get quite as cool.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
A dry cold front will cross through the region by Tuesday, leading
to cooler temperatures behind the front due to a northerly component
in the winds. High pressure is forecasted to build over the area
from the north Wednesday, allowing dry conditions and seasonal
temperatures. As the high shifts offshore Thursday temperatures will
start to moderate across the Southeast, rising to near normal for
this time of year. Additionally, a few showers are possible
offshore, near the Gulf Stream.
.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
VFR. Gusty west to northwest winds were ebbing a bit at dusk, but
expected to ramp up again later this evening as low level cold
air advection increases. Winds will slacken off overnight at both
Extended Aviation Outlook: VFR.
Tonight: Strong cold air advection will spread over the area in
the wake of a cold front. Expect solid Small Craft Advisory
conditions for all waters with some gale force gusts near 35 kt
possible, mainly off the Charleston County coast and beyond 20 nm
elsewhere, but not enough to warrant a Gale Warning. Seas will
build to 2 ft within CHS harbor, 6 ft within 20 nm and 8 ft in the
GA offshore waters, generally highest to the east given the
Saturday through Sunday: Lingering cold advection and steady
isallobaric pressure rises will keep the ongoing Small Craft
Advisories in effect through late morning or early afternoon. As
high pressure builds from the lower Mississippi Valley later
Saturday and into the southeast states Sunday, more relaxed marine
conditions will take hold over the coastal waters.
Monday through Wednesday: High pressure along the Gulf coast
gradually becomes absorbed by a much larger and stronger area of
high pressure building out of southern Canada and the western Great
Lakes. An east-west aligned cold front will move in from the north
late in the day or early at night, followed by the aforementioned
high building into it`s wake. Modest pressure rises and a tightening
of the gradient behind the front might allow for another round of
Small Craft Advisories into the middle of next week.
SC...Lake Wind Advisory until 8 AM EDT Saturday for SCZ045.
MARINE...Small Craft Advisory until noon EDT Saturday for AMZ350-352-
Small Craft Advisory until 2 PM EDT Saturday for AMZ374.
Small Craft Advisory until 8 AM EDT Saturday for AMZ330.