Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 291947
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
347 PM EDT Sat Apr 29 2017

.SYNOPSIS...
High pressure will extend across the region through Monday. A
cold front will move through early Tuesday with a stronger storm
system to affect the area late next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Atlantic high pressure will holds its influence on the region
tonight. Conditions favor another round of low stratus overnight
with low-level moisture being advecting inland from off the
Atlantic. The boundary layer looks to remain coupled through the
night, so fog should not be an issue. It will be another warm
and humid night for late April with lows ranging from around 70
inland to the lower-mid 70s at the coast. The record high
minimums at all three climate sites could be challenged.

&&

.SHORT TERM /SUNDAY THROUGH TUESDAY/...
Sunday: Deep layered high pressure over the Atlantic will extend
west over much of the Southeast United States well ahead of deep low
pressure system shifting over the Central United States. The pattern
will result in mainly dry and warm conditions over much of the area
with afternoon temps peaking in the mid/upper 80s away from the
coast. A few models suggest weak h5 shortwaves sliding along the
western periphery of the ridge over the area, which could be enough
forcing to produce a few afternoon showers and/or thunderstorms well
inland. However, confidence remains too low to include in the
forecast at this time. Overnight lows will remain mild, ranging in
the upper 60s to lower 70s.

Monday: Deep layered ridging will slowly retreat east over the
Atlantic as a large area of low pressure lifts northeast over the
Midwest. A southward extending cold front associated with this low
will make a run toward the Southeast United States late, likely
losing some speed as it becomes further separated from the parent
low. Deep moisture advection and ample sfc heating is anticipated
within a southerly flow ahead of the front, which should lead to
scattered showers and thunderstorms during afternoon/evening hours.
In general, high temps should peak in the mid 80s. The pressure
gradient will also tighten over the area ahead of the approaching
front Monday, suggesting gusty wind potential (near 30 mph) when
afternoon heating promotes mixing into 40 mph low-lvl winds fields.
A Lake Wind Advisory could eventually be needed Monday afternoon for
gusts around 25 kt over Lake Moultrie.

The bulk of precip activity should occur during Monday night when
fropa occurs. At this time, severe weather is not anticipated, but
thunderstorms will be likely across the region. Overnight lows
should range in the upper 50s inland late to lower/middle 60s closer
to the coast.

Tuesday: High pressure will build over the Southeast behind the
departing cold front offshore. Expect all areas to be dry and temps
to be slightly cooler than the previous day. In general, afternoon
temps will peak in the lower 80s with a few mid 80 temps well
inland.

&&

.LONG TERM /TUESDAY NIGHT THROUGH FRIDAY/...
Generally drier/cooler weather through Wednesday before rain chances
return with the approach of a stronger storm system toward the end
of the week. Quite a bit of uncertainty remains regarding this
system so forecast confidence is lower than normal. Conditions look
at least marginally favorable though for some stronger storms
Thursday. Temperatures should be near or above normal through at
least Thursday night before likely dropping below normal
Friday/Saturday.

&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
VFR this evening at both KCHS and KSAV with increasing
probabilities for IFR cigs overnight. Timing for IFR is a bit
uncertain, but most guidance agrees that low clouds will fill in
later this evening and persist overnight. Right now the thinking
is that cigs will remain above alternate minimums. Conditions
are expected to return to MVFR by mid-morning with VFR by late
in the 18z TAF period.

Extended Aviation Outlook: Low chances of flight restrictions at
KCHS/KSAV Sunday night. Ceiling and/or visibility restrictions are
likely Monday into late Monday night due to low clouds, showers and
thunderstorms. Breezy/gusty conditions are also expected Monday
ahead of an approaching cold front. Another round of flight
restrictions is possible Wednesday night/Thursday.

&&

.MARINE...
Tonight: Quiet conditions with south to southeast winds
prevailing. Some light nocturnal jetting could support a few
hours of 15-20 kt over the Georgia offshore waters early Sunday,
but winds will generally remain 10-15 kt across the nearshore
waters. Seas will average 2-3 ft nearshore and 3-4 ft offshore.

Sunday through Thursday: Deteriorating conditions are expected
Sunday while a cold front progresses toward the Southeast United
States. At this time, a Small Craft Advisory could be needed for the
CHS Harbor when a seabreeze circulation develops near the land/sea
interface Sunday afternoon. A Small Craft Advisory could also be
needed for offshore Georgia waters late Sunday afternoon when seas
approach 6 ft beyond 40 nm. However, the greatest potential for
Small Craft Advisory level conditions will be Monday into Monday
night when winds gust near 25-30 kt and seas build up to 6-8 ft.
Small Craft Advisories will likely be needed for all waters until
fropa nears/occurs Monday night into early Tuesday. Otherwise, no
significant issues are anticipated until Wednesday night/Thursday
when another cold front approaches.

&&

.TIDES/COASTAL FLOODING...
Latest tide trends indicate levels are remaining very close to
predicted values this afternoon, maybe running just slightly
above. The GFS-based extratropical storm surge guidance is
running too high, especially at the Charleston Harbor gage. Will
not issue a Coastal Flood Advisory with the late afternoon
forecast package as high tide will not occur until very late
this evening and there is still plenty of time to evaluate tidal
trends.

Elevated tides are expected to continue into Sunday, aided by
persistent onshore winds. Minor saltwater inundation is possible
during the high tide Sunday night along the South Carolina
coast.

&&

.CLIMATE...
Record high minimums for 29 April:
KCHS: 72/2014.
KCXM: 75/2002.
KSAV: 74/2014.

Record high minimums for 30 April:
KCHS: 69/2014 and previous years.
KCXM: 73/1912.
KSAV: 72/1953 and previous years.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$


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