Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 212248

Area Forecast Discussion
National Weather Service Charleston SC
648 PM EDT Wed Mar 21 2018

High pressure will prevail through Saturday. A cold front will
drop through the area on Sunday with high pressure then
building in from the north through the middle of next week.


Cold air cumulus will dissipate after sunset with the loss of
insolation. Expect mostly clear skies to prevail overnight with
lows ranging from the mid 30s well inland to the upper 30s/lower
40s at the beaches. Winds will also diminish slightly, but a
fairly tight pressure gradient will keep winds mostly elevated
through the night. The risk for frost is pretty small, except
well inland where there is a chance for winds to drop off just
enough before sunrise to allow some patchy frost to develop in
outlying and wind sheltered areas.

The Wind Advisory has been allowed to expire and a Lake Wind
Advisory remains in force for Lake Moultrie through 10 pm.

Local Storm Reports and a Public Information Statement have
been issued outlining peak winds observation recorded today.


A strong upper trough will gradually shift offshore Thursday
into Friday while Canadian high pressure sinks southeast into
the area. Mostly clear skies will be the rule both days. Cold
air advection will continue on Thursday, yielding high temps in
the low to mid 60s. Friday should be a few degrees warmer due to
the air mass gradually modifying. Friday morning should be
quite chilly, especially away from the immediate coast, due to
strong radiational cooling. Lows in the mid 30s far inland along
with light and variable winds should allow for the formation of
patchy to scattered frost. A Frost Advisory may eventually be

Shortwave energy will pass the area to the north on Saturday. A
warm front will develop just north of the forecast area, likely
keeping rain chances out of the local zones. We do expect
increasing mid and high clouds during the day, primarily across
southern SC. Otherwise, temps should warm considerably as
southerly flow develops and warm air advection begins. Highs
will range from middle 70s to the south to middle 60s north.


Models are in good agreement on the synoptic pattern through
the long term period. A cold front is progged to drop south
through the forecast area on Sunday, as high pressure wedges in
from the north. Some rain will accompany the front, although
models vary on coverage so have capped PoPs in the 30-40% range.
A wedge-like setup will persist through Monday with clouds and
cool northeast flow keeping temperatures below normal. On
Tuesday, the high will begin to expand over the area and help
temperatures moderate closer to normal.



Extended Aviation Outlook: VFR through Saturday. Sub-VFR
ceilings possible Saturday night through Monday as a front drops
into the area.


Downgraded the Gale Warning to a Small Craft Advisory for
Charleston Harbor. Pilot Boat and buoy reports show frequent
gusts to gale force continue across the nearshore and offshore

Tonight: Winds will begin to slowly decrease this evening as
pressure rises slow and the pressure gradient relaxes. The Gale
Warning will first come down in Charleston Harbor at 23z,
followed by the nearshore waters around midnight, and then the
early morning for the outer Georgia waters. Solid Small Craft
Advisory conditions will remain after the Gale Warnings, so
advisories will replace the warnings when they come down. By
late tonight, winds will generally be 20-25 knots, with gusts up
to 30 knots. Seas will decrease accordingly with the wind, with
5-6 seas become increasingly limited to areas beyond 20 nm.

Winds and seas will drop off quickly on Thursday, though Small
Craft Advisory conditions will probably persist through at least
the morning hours over some of the coastal waters. Conditions
will then be fairly quiet through Friday night before southerly
winds strengthen on Saturday as the surface high shifts
offshore. The gradient will increase considerably during the day
Saturday and a late day sea breeze enhancement could provide
additional enhancement along the coast. Some gusts to 20 kt
possible in Charleston Harbor late in the day.

A cold front will drop south through the waters on Sunday as
high pressure wedges in the from the north. Marine conditions
will deteriorate, and Small Craft Advisories will be possible
beginning Sunday evening and persisting through Monday.


SC...Lake Wind Advisory until 10 PM EDT this evening for SCZ045.
MARINE...Gale Warning until midnight EDT tonight for AMZ350-352-354.
     Gale Warning until 4 AM EDT Thursday for AMZ374.
     Small Craft Advisory until 2 AM EDT Thursday for AMZ330.


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