Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 171801
AFDCHS

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

.SYNOPSIS...
An arctic cold front will push offshore today. Cold, dry high
pressure will prevail across the region Thursday 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 /UNTIL 6 PM THIS EVENING/...
Early afternoon radar trends indicate precip was steadily
diminishing. This will continue through the afternoon. We have
gotten a few sleet/snow reports far inland, and a light wintry
mix may continue for the next couple of hours far inland before
drying out. No accumulation is expected. Further east near the
coast and to the north, the colder air and moisture don`t
coincide, so light rain will be the primary p-type.

Another tricky aspect to the forecast has been temperatures. Our
high temperatures in the interior zones was likely reached this
morning and will now decline/remain steady the rest of the day.
Near the coast, especially across northern zones, temperatures
have been able to soar to the low 50s where cloud cover and
colder air had not yet arrived. Thus a decent gradient exists.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
Tonight: Light precipitation looks to linger across the
Charleston Tri-County area into Colleton County this evening as
the base of the large, upper trough swings through. Freezing
levels will drop enough during this time to support a few light
snow showers or flurries, but no accumulation is expected as
moisture will be quickly thinning with time. Mostly clear skies
will prevail overnight the last of the clearing pushes off to
the northeast with the upper trough. The various statistical
guidance members look to be running a degree or two too warm
given gusty winds will keep the boundary layer well mixed
through the night. Expect lows to bottom out in the lower 20s
inland with mid-upper 20s at the coast. Wind chills will lower
to around 15 degrees across the coastal counties by daybreak
Thursday. The situation looks a bit too marginal for a second
period Wind Chill Advisory, so will defer to the day shift to
determine whether one will be needed. Inland wind chills look to
remain above advisory criteria.

Thursday through Saturday: Dry sfc high pressure will build
over the Southeast on Thursday behind a mid/upper lvl trough
departing off the eastern seaboard. The setup will support temps
well below normal Thursday afternoon with highs peaking only in
the mid 40s. Thursday night lows will be chilly under clear
skies and a light westerly wind, dipping into the mid 20s away
from the coast. On Friday, noticeably warmer conditions are
expected as dry high pressure becomes more centered near the
area Friday afternoon. In general, temps should peak in the mid
50s under a full sun and ridging aloft. Friday night lows should
dip into the lower 30s away from the coast. A mid/upper lvl low
is then expected to traverse the Southeast on Saturday, but
moisture will be very limited, especially in the lower levels
where dry high pressure remains. Given the setup, some mid/upper
lvl clouds are possible as the disturbance passes aloft, but
precip is not expected over the area. Temps will continue to
modify during the weekend. In general, highs should peak in the
lower 60s Saturday afternoon.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
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 /18Z WEDNESDAY THROUGH MONDAY/...
Some low clouds are lingering behind a cold front that pushed
offshore this morning. There could be a brief period of sub-VFR
cigs this afternoon and have included best timing in the TAF.
Also couldn`t rule out light precip at KCHS this afternoon/early
evening. Conditions will improve tonight and VFR is expected by
early Thursday morning.

Extended Aviation Outlook: VFR conditions are expected at both KCHS
and KSAV terminals Thursday afternoon through Sunday.

&&

.MARINE...
Today: Conditions will deteriorate across the waters today
behind a cold front. Northwest winds will increase this
afternoon to 15-20 kt with seas building 2-4 ft nearshore and
as high as 4-6 ft over the Georgia offshore waters. A Small
Craft Advisory is now in effect for the GA waters. SC waters
won`t be far behind, with advisories starting late this
afternoon.

Tonight: Winds will peak 20-25 kt with gusts to 30 kt across all
waters as an arctic airmass settles in across the region. A
Small Craft Advisory will be issued for all areas outside of the
Charleston Harbor. Conditions in the harbor look to peak just
shy of advisory thresholds. Seas will peak 3-5 ft nearshore
waters and 5-7 ft offshore waters.

Thursday through Monday: Winds/seas will decrease/subside Thursday
as cold air advection begins to wane over coastal waters. However, a
Small Craft Advisory will likely be ongoing to around noon while 6
ft seas linger in offshore Georgia waters. Dry high pressure will
then dominate/prevail over the coastal waters this weekend into
early next week with winds/seas remaining well below Small Craft
Advisory levels. In general west/northwest winds will remain at or
below 15 kt Friday through Sunday while seas are no higher than 2-3
ft. A southerly wind will then develop on Monday as a cold front
approaches from the west late in the day. Expect winds and seas to
increase/build, but remain below Small Craft Advisory levels during
fropa.

&&

.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...None.
SC...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 5 AM EST
     Thursday for AMZ350-352.
     Small Craft Advisory until 1 PM EST Thursday for AMZ374.
     Small Craft Advisory until 5 AM EST Thursday for AMZ354.

&&

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



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