Area Forecast Discussion
Issued by NWS Charleston, SC

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710
FXUS62 KCHS 252101
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
401 PM EST Sat Feb 25 2017

.SYNOPSIS...
Cool high pressure will build into the region through Sunday. The
high will then shift offshore early next week as a warm and moist
air mass builds from the Atlantic and Gulf of Mexico. Another cold
front will move through Wednesday night into Thursday, followed by
high pressure for the end of next week.

&&

.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Until Sunset: Satellite and surface observations indicate the
cold front is crossing our forecast area. The only remaining
impact will be some clouds and the gusty winds. As sunset
approaches, the skies will clear and the winds should begin to
ease.

Tonight: Cold advection quickly fills in behind the departing
cold front. A gigantic diurnal swing in temps will transpire,
with lows by Sunday morning down some 40 F colder than they
were today. Tonight will be the coldest night for many of us in
about a week, as high pressure builds in from the W. Lows will
range from the upper 30s to lower 40s.

&&

.SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
Sunday and Sunday night: Benign and fast west-southwest flow will
prevail aloft through Sunday night. At the surface, cooler high
pressure will shift across the southern Appalachians during the day,
then off the East Coast overnight. Deep dry air will prevail through
the period and clear skies are expected until perhaps very late
Sunday night. Temperatures will be considerably cooler than the
record breaking warmth we have experienced the past few days.
However, highs are expected to be in the low to mid 60s which would
only be at or slightly below normal for late February. Overnight
lows will fall into the low to mid 40s in most areas, with a few
upper 30s possible well inland and across the Francis Marion.

Monday through Tuesday: The pattern aloft will not change
significantly during the early part of the week and will still
feature west-southwest flow. The main difference from Monday will be
the presence of embedded shortwave energy poised to move along the
Gulf Coast and across the forecast area late Monday and Monday
night. As this series of impulses moves through, an area of low
level convergence and increased moisture will surge into southeast
Georgia late Monday. This area of forcing will then move along the
coast Monday night. No significant changes were made to the going
PoP scheme as there is still enough uncertainty with model solutions
to prevent introducing higher rain chances. The 25/12z run of the
ECMWF is now essentially dry and keeps the best coverage offshore.
The GFS has more rainfall across land areas, but still seems to
favor southeast Georgia and then the Atlantic coastal waters.
By Tuesday, the organized rain chances will end and we may see a few
diurnal showers/thunderstorms in the afternoon. Temperatures will
moderate impressively each day. Highs are expected to be back into
the mid 70s by Monday and then upper 70s/low 80s by Tuesday.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
A long wave upper trough will advance from the Great Plains to the
Tennessee Valley Tuesday night through Thursday. There is decent
model agreement that an advancing cold front will reach the forecast
area either late Wednesday night or early Thursday with the GFS
running just a tad faster than the ECMWF. March will come in with
potential record warmth given 13C-15C 850 MB temps in southwest
synoptic flow. High temps could soar to the mid 80s with periodic
breaks in the clouds. Higher rain chances should come ahead of the
cold front either Wednesday night or early Thursday. Despite
increasing deep layered shear on Wednesday and Wednesday night,
severe potential still looks rather low-end due to model differences
in frontal timing and marginal instability. In the wake of the
front, cooler and closer to climo temps are expected Friday and
Saturday with dry weather both days.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
VFR. Gusty W-NW behind the cold front will continue into early
this evening, then ease.

Extended Aviation Outlook: VFR through Monday morning. Flight
restrictions possible late Monday and Monday night with low
clouds/showers. Morning stratus possible Tuesday and Wednesday.
A cold front will move through Thursday, brief restrictions
possible in clouds/showers.

&&

.MARINE...
Tonight: The cold front will move across the coastal waters
early this evening. Cold advection behind the front overnight
combined with decent pressure rises will lead to rising winds
across all of the coastal waters. Gusts should be 25 kt for a
few hours, so Small Craft Advisories are now in effect.

Sunday through Thursday: High pressure will pass by to the north of
the local waters on Sunday. As it does, northerly flow will veer
around to become easterly by Monday morning. Winds/seas will be much
improved and the only lingering Small Craft Advisory will be for the
outer Georgia waters. This advisory will then likely come down
Sunday morning. Then Monday through Tuesday onshore southeasterly to
southerly flow will prevail, with a modest 10-15 knots of wind
prevalent. Locally, speeds could be a bit stronger along the coast
with the sea breeze development each afternoon. Southerly to
southwesterly flow will prevail into Thursday ahead of the next
front, and conditions could become favorable for sea fog
development. Confidence is too low to mention in the forecast at
this time though. A cold front moving into the waters on Thursday
should result in an uptick in wind and seas with unfavorable mixing
profiles until cold air advection ensues post front. Advisory
conditions may be possible.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until 11 PM EST this evening for SCZ045.
MARINE...Small Craft Advisory from 11 PM this evening to 3 AM EST
     Sunday for AMZ352-354.
     Small Craft Advisory until 9 AM EST Sunday for AMZ374.
     Small Craft Advisory from 9 PM this evening to 3 AM EST Sunday
     for AMZ350.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...
AVIATION...
MARINE...
CLIMATE...



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