Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 180014
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
714 PM EST Wed Jan 17 2018

.SYNOPSIS...
Cold, dry high pressure will build into the region and prevail
into Friday before moderating temperatures occur this weekend
into early next week. A cold front will push through the area
Monday, followed by dry high pressure into the middle of next
week.

&&

.NEAR TERM /THROUGH THURSDAY/...
A cut-off upper low over the western Carolinas will swing east
tonight and will be off the NC coast by Thursday morning. The
associated embedded short wave will pivot through the first
part of the night, when our best height falls occur. Meanwhile
at the surface, high pressure will build in from the west as low
pressure lifts to the northeast.

Considerable moisture remains trapped beneath the low level
inversion within the cyclonic flow, especially over the northern
half of the forecast area. But with the passage of the short
wave aloft and an anticyclonic flow developing late evening and
overnight, moisture is stripped out and skies will clear.

Meanwhile, there is already freezing temps above about 1000 ft
this evening, and colder air will continue to filter in
underneath and at the surface. During this transition there will
be a little light rain or sprinkles over parts of the Charleston
tri-county district that mixes with or even changes over to very
light snow or flurries. This is only a novelty and no impacts
will occur, with absolutely no accumulations. We have slight
chance PoP through about 11 pm to midnight as a result.

Strong cold advection will take hold tonight with temperatures
dropping to the low-mid 20s. These temperatures will combine
with elevated winds to produce wind chills in the mid teens.
Given the coastal county wind chill advisory criteria is 15
degrees, we have an advisory for 4 AM to 8 AM. Conditions
elsewhere (inland) are not expected to meet their respective
criteria of 10 degrees.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/...
Cold, dry high pressure will continue to build in behind a
sharp upper shortwave trough Thursday, then prevail into Friday
before temperatures moderate to above normal levels Saturday.
Many areas will start Thursday morning in the lower to mid 20s
and this will cause wind chills near 15 degrees. Most areas will
be back into the 20s Friday morning, even close to freezing at
the coast.

&&

.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
High pressure will prevail over the Southeast United States late
weekend into early next week before a cold front arrives Monday. The
pattern will favor warming conditions under ridging aloft. In
general, afternoon highs will peak in the mid/upper 60s on Sunday.
By Monday, southerly winds will help advect deep moisture over the
Southeast and produce some cloud cover ahead of the approaching
front. This could limit overall heating potential, but a prevailing
southerly flow should still support temps in the upper 60s for most
locations in Southeast South Carolina to around 70 degrees in
Southeast Georgia ahead of cold front. Chances of showers should
arrive to most areas Monday afternoon as the front begins to shift
over the region. Dry high pressure will then return on Tuesday and
persist into the middle of next week. Temps will be slightly cooler
behind the front, but should remain a few degrees above normal. In
general, Tuesday and Wednesday afternoon temps should peak in the
lower 60s. Overnight lows should range in the low/mid 40s.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
Low level moisture will remain trapped at KCHS through much of
the night, equating to low-end VFR or high-end MVFR ceilings
through 09Z. VFR returns thereafter. There could be a little
very light rain or very light snow at the terminal early in the
TAF period, but no impacts will occur.

At KSAV there could be a period of low-end VFR ceilings from
about 03-07Z, otherwise VFR will prevail.

Both sites will experience gusty NW winds tonight, generally in
the 10-20 kt range with some higher gusts.

Extended Aviation Outlook: No significant concerns.

&&

.MARINE...
Based on NW winds of 20-25 kt at Ft. Sumter and forecast
soundings showing similar values, we have gone ahead and raised
a Small Craft Advisory for Charleston Harbor with the evening
update.

Strong pressure rises and ongoing cold advection will result in
Small Craft Advisories for all Atlantic waters tonight. NW winds
will peak in the 15-25 knot range with gusts of 25-30 kt. Seas
on average will be 3 to 5 feet nearshore, 5 to 7 feet in the
outer waters.

Thursday through Monday: Winds/seas will improve Thursday as the
pressure gradient and cold advection wane, with the offshore waters
dropping below Advisory levels in the early-mid afternoon. No other
significant concerns thereafter through next Monday.

&&

.EQUIPMENT...
The KCLX radar is out of service until further notice. Repairs
are ongoing. Adjacent radars include: KLTX, KCAE, KJGX, KVAX
and KJAX.

The Downtown Charleston observation site (CHLS1/KCXM) remains
out of service until further notice.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Wind Chill Advisory from 4 AM to 8 AM EST Thursday for
     GAZ116>119-137>141.
SC...Wind Chill Advisory from 4 AM to 8 AM EST Thursday for
     SCZ048>052.
MARINE...Small Craft Advisory until 7 AM EST Thursday for AMZ350-352-
     354.
     Small Craft Advisory until 1 PM EST Thursday for AMZ374.
     Small Craft Advisory until 4 AM EST Thursday for AMZ330.

&&

$$
NEAR TERM...
SHORT TERM...RJB
LONG TERM...
AVIATION...
MARINE...
EQUIPMENT...


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