Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 211451

Area Forecast Discussion
National Weather Service Charleston SC
1051 AM EDT Wed Mar 21 2018

High pressure will build in from the west today and prevail
through Saturday. A cold front will drop south through area on
Sunday. High pressure will return early next week.


Late this morning: The main forecast concern today is the
strength of surface winds around the deepening surface low off
the Mid Atlantic coast. Low level winds are quite strong, with
35+ knots noted only a 2-3 kft off the surface. With mixing
expected to tap into belt of stronger winds, the Wind Advisory
has been expanded to include the South Carolina coast in
addition to the previously included areas in southeast Georgia.
Wind gusts to 40 mph will be possible and this could cause
isolated trees to come down and could make travel difficult on
areas bridges. Otherwise, made some adjustments to sky cover
based on visible satellite imagery which shows some lower clouds
approaching from the northwest within the wrap around.
Otherwise, the forecast is in good shape.

Tonight: Models suggest a gradient wind will tend to persist
across the region but we think far inland areas may have a
chance to decouple late. Even if some cooler inland areas
dip to the mid 30s late, frost potential appears too poor at
this time to intro any frost mentions. The cool temps will feel
chillier early Friday with light breezes along the coastal

Lake Winds: We extended the advisory for Lake Moultrie a bit
longer into the early evening hours.


Expansive area of low pressure off the New England coast will lift
northeast, allowing high pressure to continue to build in from the
west Thursday and Friday. Aloft, broad troughing will persist over
the east coast. Deep dry air will keep skies mostly clear and rain-
free conditions. Despite little to no cloud cover, cool northwest
flow will limit heating. Temperatures are forecast to stay below
normal, with highs peaking in the 60s. Good radiational cooling
setup for Thursday night, with winds expected to drop off late. As
low temperatures drop to the mid 30s inland late, some patchy frost
could develop. Lows Friday night will be more mild in the 40s with
no frost concerns.

The surface high will drift overhead and then into the Atlantic on
Saturday as an area of low pressure drops out of the Midwest into
the Ohio River Valley. Some moisture return expected as flow turns
southerly, but nothing more than an increase in cloud cover
expected. Temperatures will moderate some with highs forecast to
range from the mid 60s across northern zones to mid 70s near the


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.


VFR. Gusty WNW winds will impact the terminals into the early
evening hours today. Gusts will likely reach 35 kt at times
through the afternoon hours at both KCHS and KSAV. Winds will
diminish overnight.

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


Late this morning: We maintained current Gale Warnings for the
coastal waters and expanded the warning into the Charleston
Harbor. Strong jetting offshore flow will tend to be a bit
stronger to the south of Charleston but hazardous conditions are
expected in all near shore waters today. Gusts should top 40 kt
well offshore over outer 20-60 NM GA waters where seas will be
in the 6-9 ft range. Down river locations such as Fort Pulaski
GA should have excellent exposure to surging and jetting
conditions today and gusts to 35 kt may be common there today.

Tonight: The Gale warnings should be lowered to SCA in our near
shore waters but frequently gusts to 35 kt are expected closer
to the Gulf Stream.

Thursday through Monday: High pressure will continue to build in
from the west Thursday into Friday. Elevated pressure gradient will
keep northwest winds around 15 knots on Thursday, before it slackens
on Friday. The high will shift overhead and then into the Atlantic
on Saturday allowing winds to become more southerly.  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.


GA...Wind Advisory until 7 PM EDT this evening for GAZ116>119-
SC...Wind Advisory until 7 PM EDT this evening for SCZ048>052.
     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.
     Gale Warning until 7 PM EDT this evening for AMZ330.



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