Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 161213
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
713 AM EST Tue Jan 16 2018

.SYNOPSIS...
High pressure will linger over the region today. A cold front
will sweep across the area Wednesday morning, followed by dry
high pressure into late week. Warmer conditions arrive this
weekend before another cold front pushes through Monday. Dry
high pressure will then return on Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: High pressure will continue to break down across our
region with morning sunshine warming temps by midday to the
upper 40s north to around 50 degrees across southeast GA. An
advancing cold front will be moving in far northwest GA late and
strengthening upper jets across the region will likely result
in increasing/expanding cirrostratus clouds by this afternoon,
especially late in the day. We maintained highs in the mid 50s
most areas with a few upper 50s possible around the lower
Altamaha River region.

Tonight: Clouds will continue to thicken and increase ahead of the
cold front and this should hold temps above freezing most areas
tonight, although we could see a few of our colder inland spots
touch freezing if clouds fail to thicken earlier than later. A
deep upper trough is forecast to dig into the lower Gulf Coast
region overnight, driving the cold front into the forecast area
prior to daybreak. We introduce some slight chance POPs across
far inland GA and SC zones bordering the CSRA. Model forecast
soundings suggest light rain and sleet could mix prior to dawn
in this area as band of enhanced moisture accompanies the frontal
zone. No accumulations are expected in the overnight period.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
Wednesday: A cold front will quickly shift through the area early
morning with strong cold air advection in its wake. Guidance
continues to show the bulk of precip occurring over the area well
behind the sfc cold front where strong upper lvl divergence occurs
with a passing h25 jet aloft. Timing will be key in regards to rain
and/or mixed precipitation well inland, possibly in the form of
light snow/flurries or sleet. The main issue will be how cold the
boundary layer becomes as moisture quickly traverses the area, then
departs to our north and offshore by early afternoon. Clouds should
keep sfc temps above freezing during morning hours for all areas,
but most guidance suggests air will be cold enough off the sfc to
produce some snow flurries or sleet over inland areas for a few
hours Wednesday morning. Locations along and west of the I-95
corridor in Southeast South Carolina and well inland and north of I-
16 in Southeast Georgia should have the greatest chance of seeing
precip in the form or snow or sleet. However, any wet snow
flakes/flurries/sleet will likely melt quickly once it reaches the
sfc, thus no accumulation is expected. Dry high pressure entering
from the west should put an end to most if not all precip by early
afternoon. However, if any precip lingers over the Tri-County area
it will likely remain in the form of light rain. Afternoon temps
will remain well below normal behind the cold front. In general,
temps will peak in the low/mid 40s around noon, then follow a
cooling trend into the evening.

The next issue will turn to wind chill temps Wednesday night. Dry
high pressure will lead to clear skies and sfc temps that cool off
rapidly. In general, temps should dip into the low/mid 20s over most
areas. These temps along with a light northwest wind could produce
wind chill values near 15 degrees across the area. A Wind Chill
Advisory could be needed for coastal counties.

Thursday and Friday: Dry sfc high pressure will build over the
Southeast behind a mid/upper lvl trough departing off the East Coast
on Thursday. The setup will support temps well below normal on
Thursday with afternoon highs peaking only in the mid 40s. Thursday
night lows will be chilly under clear skies, dipping into the mid
20s away from the coast. By Friday, noticeably warmer conditions are
expected as dry high pressure becomes centered over or near the
area. In general, temps should peak in the mid 50s Friday afternoon
under a full sun and ridging aloft.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
High pressure will prevail over the Southeast United States this
weekend and early next week before a cold front arrives Monday. The
pattern will favor warming conditions each day under ridging aloft.
In general, afternoon highs will peak in the lower 60s on Saturday,
then upper 60s to around 70 degrees 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 should limit
overall high temps to the upper 60s for most locations. Chances of
showers will arrive to most areas by Monday afternoon as the front
begins to shift over the region. Dry high pressure will then return
on Tuesday behind the departing cold front. Temps will be cooler,
but should remain at or just a few degrees above normal. In general,
afternoon temps should peak in the lower 60s.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
VFR at KCHS/KSAV through 12Z Wednesday.

Extended Aviation Outlook: VFR conditions are expected at both CHS
and SAV terminals Wednesday afternoon through Saturday. A cold front
could bring gusty winds at both terminals Wednesday afternoon.

&&

.MARINE...
Winds will be light and occasionally variable close to shore
today, as high pressure weakens over the forecast area. Northeast
flow will prevail off the coast with speeds mostly less than 10
kt. There is still some lingering swell wave and seas will continue
to be a bit elevated, 2-4 ft within 20 NM and 3-5 ft well offshore.
Winds will likely back offshore late as a cold front moves in late.
Prior to sunrise, there may be the beginning of a surge off the
GA coast with speeds increasing to 15 kt. Otherwise, light winds
and seas ranging 2-3 ft near shore and 3-5 ft beyond 20 NM off
the GA coast.

Wednesday through Sunday: Winds/seas will remain below Small Craft
Advisory levels Wednesday morning while high pressure persists over
coastal waters ahead of a quickly approaching cold front. Conditions
are then expected to deteriorate Wednesday afternoon/evening as
strong cold air advection occurs behind the passing cold front.
Small Craft Advisory level conditions are likely for most waters
outside the CHS Harbor by Wednesday evening and should continue into
early Thursday morning. Winds/seas will then diminish/subside
through much of Thursday as the pressure gradient weakens in
response to high pressure building over the waters. High pressure
will dominate the weather pattern over the weekend into early next
week, supporting conditions that remain well below Small Craft
Advisory levels.

&&

.EQUIPMENT...
The KCLX radar is out of service until further notice. Technicians
are troubleshooting and working on repairs.

The Downtown Charleston observation site (CHLS1/CXM) will be
unavailable until further notice.

&&

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

&&

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



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