Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 240237

Area Forecast Discussion
National Weather Service Charleston SC
1037 PM EDT Mon Apr 23 2018

Low pressure will shift over the area tonight, then slowly move
up the east coast through mid week. An upper disturbance will
move over the area Thursday night, followed by a cold front
late week. High pressure will return over the weekend.


Radar indicates the bulk of the deep moisture is currently over
the Charleston-Tri County area and moving northward. Further
west, far inland, there is a band of showers and thunderstorms.
SPC mesoanalysis shows MLCAPEs around 1,000 J/kg in this area
along with 0-6 km shear ~40 kt. However, CAM`s indicate the
atmosphere becoming more stable in this area in the upcoming
hours as we lose the heating of the day. For the upcoming 1-2
hours, gusty winds and maybe small hail are the immediate
concern in these thunderstorms. But then conditions will improve
afterwards as the synoptic and mesoscale pattern becomes less
favorable for convection.

Synoptically, the deep upper low and attending surface low
centered over Tennessee will slowly lift to the northeast. As
this occurs, a warm front will continue to lift northward
through the forecast area the rest of this evening and
overnight, pushing away the moisture and being backfilled by
drier air. Skies will be cloudy, though portions of southeast
Georgia could start to scatter out late. It will be a mild night
with lows only falling into the low to mid 60s. Winds will
remain strong and gusty into the Charleston County for a few
more hours, then easing overnight.


Tuesday: A cold front will be offshore by daybreak, shifting
northeast and further offshore while an area of sfc low pressure
tracks along/near the Mid-Atlantic coast. A trailing mid/upper
lvl low to the west/northwest will slowly meander over the
Southeast during the day, then shift over the Mid-Atlantic
states late day and night. The overall pattern suggests mostly
dry conditions and less cloud cover. However, a few showers can
not be ruled out across northern and inland areas in Southeast
South Carolina, as the mid/upper lvl low shifts just north of
the area. Overall highs will be slightly warmer, peaking in the
upper 70s under partly cloudy skies. Overnight lows will be
fairly mild, ranging in the mid/upper 50s away from the
immediate coast.

Wednesday: The main mid/upper lvl low will continue to shift
east- northeast and away from the area, setting up dry
conditions and mostly sunny skies as high pressure temporarily
shifts into the region and a downsloping wind component occurs
over the Southeast. Overall highs should be a degree of two
warmer than the previous day with more sun. In general, highs
should peak in the upper 70s to around 80, warmest along and
east of the I-95 corridor. Temps will remain mild overnight,
ranging in the mid/upper 50s away from the immediate coast.

Thursday: The next best chance of rainfall should occur with a
low pressure system that quickly advances over the Deep South
and to the Southeast United States. Latest trends suggest much
of the area will remain dry during daylight hours until the bulk
of strongest forcing arrives with an h5 shortwave aloft late
day and overnight. Chances of showers have been limited to
inland areas through the afternoon, before precip activity
increases during the evening and overnight. Increasing clouds
and showers late in the day could limit overall heating
potential. In general, high temps should approach the mid/upper
70s, warmest in Southeast Georgia.


Forecast confidence in the extended period continues to be low
given large spread in model guidance. General consensus is that
a cold front will cross the area late week/early weekend. Given
the uncertainty on details, have kept PoPs pretty low until
trends become clearer. Models come into better agreement on
Sunday with a return to high pressure. Temperatures through the
period will generally be near normal, perhaps slightly cooler on


00Z TAFs:
KCHS: The main portion of deep moisture has moved north of the
terminal. Periods of -SHRA should continue for the first few
hours in the TAF period followed by drying conditions. IFR
ceilings are expected until around daybreak Tuesday, then VFR
will take hold. Gusty E winds will ease over the first few hours
of the TAF period.

KSAV: -SHRA or VCSH is expected for the initial part of the TAF
period, followed by drying conditions. IFR ceilings are
expected until around daybreak Tuesday, then VFR will prevail.

Extended Aviation Outlook: Flight restrictions are possible
with showers late Thursday/early Friday.


Tonight: No changes with the marine forecast. The Gale Warning
for the Charleston County waters continues and will be in place
through 2 am. Elsewhere, at least solid Small Craft Advisory
conditions are ongoing and the advisories remain in effect. Seas
remain very steep, with 41004 reporting 16 ft at 10 seconds and
41008 reporting 7 feet at 9 seconds. As the warm front lifts
northward, conditions are improving across our GA waters and
the same will be expected across the SC waters in the upcoming
hours. After midnight the gradient will be less than it is now,
allowing for lowering winds and seas.

High Surf: The High Surf Advisory continues for the Charleston
County coast through the early morning hours.

Tuesday through Saturday: Marine conditions will improve
Tuesday as a cold front and low pressure lift northeast and away
from the area. Small Craft Advisories will gradually drop as
seas fall below 6 ft, first in the southern nearshore Georgia
waters late Tuesday morning, then nearshore South Carolina
waters south of Edisto, SC early Tuesday afternoon. Higher seas
will linger in northern SC waters and offshore Georgia waters
through Tuesday night and potentially into early Wednesday
morning. Low confidence remains in the forecast late week given
model discrepancies, but it appears conditions will remain below
any headline criteria. A cold front could drop through the
waters early in the weekend, then high pressure will return for
the remainder of the weekend.


SC...High Surf Advisory until 5 AM EDT Tuesday for SCZ050.
MARINE...Small Craft Advisory until 2 PM EDT Tuesday for AMZ352-354.
     Gale Warning until 2 AM EDT Tuesday for AMZ350.
     Small Craft Advisory until 8 AM EDT Wednesday for AMZ374.
     Small Craft Advisory until 2 AM EDT Tuesday for AMZ330.


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