Area Forecast Discussion
Issued by NWS Charleston, SC

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890
FXUS62 KCHS 250605
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
105 AM EST Sat Feb 25 2017

.SYNOPSIS...
Offshore low pressure will move northeast overnight. A cold
front will cross the region Saturday, followed by cooler high
pressure Sunday. The high will shift offshore early next week.
Another cold front could move through Wednesday night into
Thursday, followed by high pressure for the end of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Fog will continue to be the main concern overnight, with patchy
to areas of fog to occur. However, strengthening low level wind
fields will likely negate any dense fog, instead transitioning
to a stratus event. A warm S-SW flow will limit temps to no
lower than 55-60F most communities.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/...
Saturday: Low pressure centered well off the Southeast coast will
shift northeast and away from the area over the western Atlantic
ahead of a cold front that approaches from the west late morning
into early afternoon hours. Ahead of the front, some patchy fog
could linger into morning hours while low-lvl moisture characterized
by sfc dewpts in the mid/upper 50s resides over the area within a
light/variable wind. However, strong sfc heating should quickly
erode fog as the inversion beaks late morning.

Breezy conditions are expected over the area by early afternoon as
record breaking temps peak into the lower 80s and tap into a 35-40
kt low lvl jet. The conditions should support a minor fire weather
concern over inland areas given deep-layered moisture is lacking and
most areas remain precip-free during the time of cold fropa Saturday
afternoon. Winds could gust up to 20-25 mph while relative humidity
values dip to around 30 percent. However, conditions should be short-
lived and marginal given recent rains to the area within the past
couple days.

Conditions will be quiet over the area Saturday night while dry high
pressure pushes into the region behind the departing cold front.
However, we could see an uptick in lake winds to 15-20 kt while cold
air advection occurs across the region. Overnight lows will be
considerably cooler than the previous night, ranging in the upper
30s inland to low/mid 40s closer to the coast.

Sunday: High pressure will become centered over the Southeast,
leading to quiet/dry conditions under a zonal flow aloft. Overall
temps will be closer to normal for this time of year. In general,
high temps will range in the low/mid 60s, warmest away from the
coast in Southeast Georgia.

Monday: Dry high pressure centered over the Southeast will slide
offshore, allowing a south/southeast wind to return moisture and
warmer temps to the region. A slight chance of showers will be
possible over most areas by Monday afternoon. However, the main
threat of thunder and heavier rains should remain offshore. Temps
will rebound considerably from the previous day, peaking in the
mid/upper 70s for areas away from the coast.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Pops raised a bit across northwest and northern zones Monday
Night as a series of mid level impulses ride through GA and the
Carolinas producing decent upper forcing across the northern
half of SC. On Tuesday and Wednesday, a strong subtropical ridge
will extend from the southwest Atlantic into the Gulf of Mexico.
Models in general agreement that the bulk of the convective pcpn
will extend west through north of the forecast area and only
slight chance pops appeared warranted. Temps still expected to
be extremely warm with highs near 80 both days away from the
beaches and barrier islands. A cold front will eventually move
through the region during mid week with chances for convective
rains. The timing of the front was still too uncertain for
entertaining any potential for strong/severe storms, neither
the GFS/ECMWF was impressive as yet. High pressure will return
for the latter portion of the upcoming week with slightly cooler
weather.

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
Shallow ground fog at bothy airfields will transition into
deeper fog/mist and areas of stratus closer to daybreak through
mid-morning Saturday, with MVFR conditions to occur. IFR and
maybe even LIFR may certainly still occur if increasing low
level winds are delayed as per latest guidance, but VFR will
return by 14Z and prevail the rest of the valid 06Z TAF cycle.

A cold front could produce a passing shower at either site
between 17Z and 20Z, but no significant impacts would occur. Of
more concern will be gusty W-SW winds that occur both in
advance of a cold front, but more especially behind the front
through sunset. Speeds will reach 15-20 kt with gusts around 25
kt during the afternoon hours.

Extended Aviation Outlook: VFR conditions are expected into
Monday. Another risk of flight restrictions is possible Monday
night with low clouds/showers, then again with a passing cold
front Wednesday night.

&&

.MARINE...
In advance of a cold front approaching from the west, winds will
turn from the east/southeast toward the south/southwest
overnight, a favorable trajectory for dewpoints in the 60s to
flow over the cool shelf waters and produce some marine
stratus/fog. However, the window for favorable trajectories/sea
fog should remain brief as winds will continue to veer through
the SW and increasingly offshore late tonight/early Saturday.
Thus, only a few hours of patchy fog are indicated in updated
public forecasts. Also, per recent observations at buoy 41004,
6 ft seas are likely persisting within 20 nm of the SC coast.
Thus, we maintained the ongoing SCA for AMZ350 until 5 am.
Otherwise, winds should remain mainly 10 kt or less overnight.
In addition to AMZ350, elevated seas emanating from offshore low
pressure will remain as high as 4-5 ft within 20 nm and 6-7 ft
beyond 20 nm. An SCA remains in effect for the outer GA waters
into Sunday morning.

Saturday through Wednesday: A Small Craft Advisory will be ongoing
in offshore Georgia waters Saturday, mainly for 6 ft seas. A cold
front will then shift over the waters Saturday afternoon through
Saturday night with strong cold air advection behind it. The setup
will likely produce wind gusts as high as 20-25 kt and seas around 6
ft Saturday night, mainly in offshore Georgia waters. However, there
is a chance of marginal Small Craft Advisory level conditions in
nearshore waters off the Charleston County coast when low-lvl mixing
is greatest. Expect conditions to improve over all coastal waters by
late morning Sunday, then remain below Small Craft Advisory levels
through midweek.

&&

.CLIMATE...
The record high for Feb 24 of 81F was tied at KCHS Friday.

High temperatures Saturday afternoon could approach record
levels for the month of February: 86F at KCHS (Feb 28 1962) and
KSAV (last set Feb 24 2012) and 83F in downtown Charleston (Feb
27 1962).

Record Highs for Feb 25:
KCHS: 80 set in 1949.
KCXM: 80 set in 1930.
KSAV: 82 set in 1985/1930.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 11 AM EST Sunday for AMZ374.
     Small Craft Advisory until 5 AM EST early this morning for
     AMZ350.

&&

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



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