Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 242340

Area Forecast Discussion
National Weather Service Charleston SC
640 PM EST Fri Feb 24 2017

Offshore low pressure will move northeast tonight. 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.


Early Friday evening: Ongoing forecasts remained on track and
required only minor adjustments...including raising sky cover to
account for smoke layer across CHS Tri-County region to start
the night.

Weakening Atlantic low pressure lifts NE to a position E of the
outer banks of NC late, as a strong cold front trailing from
robust low pressure in MI nears the spine of the Appalachians
before daybreak. Our area lies under subtle ridging surface and
aloft, with the best moisture confined closer to the cold front.
No risk for any rainfall. However, low level moisture, mostly
clear skies and condensation pressure deficits less than 20-30
mb, support the potential for fog/stratus. Probably too much
wind just above the boundary layer to produce dense fog, but
certainly enough for patchy to areas of fog to occur after
midnight. Lows will be in the mid and upper 50s with low level
warm advection within a S-SW synoptic flow.


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.


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


MVFR level smoke should dissipate over KCHS early this evening.
Otherwise, VFR until 08Z-09Z. Then, model signals are quite
strong advecting increasing low-level moisture into the region
from the south in advance of an approaching cold front late
tonight, supporting areas of stratus/fog. 00Z TAFs remain
conservative with only MVFR visibilities, scattered IFR level
clouds and BCFG by 09Z. However, IFR/LIFR conditions could
develop for a brief period toward daybreak. Then, any low
clouds/fog should give way to VFR ceilings as a cold front
crosses the region Saturday morning. In the wake of cold fropa,
expect VFR conditions and west winds gusting to 20-25 knots
Saturday afternoon.

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.


Early Friday evening: Significant changes to ongoing forecasts
were not required. The ongoing regime feating sub-SCA winds but
elevated seas produced by offshore low pressure will continue

Tonight: The Atlantic low will pass east of the area this
evening, lifting NE to off the NC coast by Saturday morning.
Winds will steadily diminish, dropping below 10 kt. Seas will
respond by slowly subsiding to 3-4 ft within 20 nm by daybreak and
up 4-6 ft across AMZ374. Small Craft Advisories should expire
for AMZ350 this evening, but remain up for AMZ374. We`ll need to
keep a close eye on fog/stratus over land that could impact the
Charleston Harbor late.

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.


The record high for Feb 24 of 81F was tied at KCHS today/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.


MARINE...Small Craft Advisory until 11 AM EST Sunday for AMZ374.
     Small Craft Advisory until 11 PM EST this evening for AMZ350.


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