Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 122344
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
644 PM EST Tue Dec 12 2017

.SYNOPSIS...
Dry high pressure will build across the region tonight and will
remain through Thursday. Another cold front will push into the
area Friday while low pressure passes offshore. High pressure
will return Saturday and persist into Sunday before a cold front
approaches the area early next week.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
Early this evening: Surface analysis and a perusal of area
observations show that the cold front has pushed offshore.
Colder air will continually spill into the region through the
rest of the night with deep dry air. Winds appear to have passed
their peak, but will likely see a secondary surge for a few
hours behind the front before the pressure gradient starts to
relax. No changes needed to the going forecast.

Lake Winds: The Lake Wind Advisory remains in effect, but based
on near term guidance could end up being cancelled early.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY/...
Wednesday and Thursday: The mid/upper levels will consist of a
trough over the eastern half of the country. At the surface,
broad high pressure generally located over the Lower MS Valley
Wednesday morning will move over FL Wednesday night, then
offshore Thursday. The air mass is dry with PWATs no more than
0.5". As for temperatures, despite sunny skies, cold air
advection will lead to below normal temperatures Wednesday and
Wednesday night. Temperatures will moderate closer to normal
Thursday and Thursday night as cold air advection wanes. Also,
expect it to be breezy along the coast Wednesday night due to a
strong gradient.

Friday: The mid/upper levels still consist of a trough over the
eastern half of the country, with a wave/disturbance stretching
from the Great Lakes region into TX in the morning. This
wave/disturbance will move eastward as the day progresses. A
weak low is forecasted to form offshore late in the day. Models
continue to indicate weak lift and little moisture across the
area, increasing slightly further offshore. As a result, we have
slight chance POPs along the immediate coast late in the
afternoon. Very little QPF, if any, is expected. Highs will be
near normal with increasing clouds.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Dry and slightly cooler high pressure will build over the
Southeast Friday night into Saturday, leading to temps in the
low/mid 30s Friday night under clear skies and highs in the
mid/upper 50s Saturday afternoon. High pressure will then become
centered over the area Saturday night, leading to strong
radiational cooling and temps that dip into upper 30s to lower
40s. Conditions will be noticeably warmer on Sunday as a light
southerly wind develops on the west side of high pressure
shifting offshore. Temps should approach the low/mid 60s Sunday
afternoon. The next chance of showers should begin Sunday night
and increase into Monday as a plume of moisture characterized by
PWATs near 1.5-1.75 inches advects over the Southeast
along/ahead of a cold front that shifts through the area Monday
evening. Temps should be fairly warm ahead of the front, peaking
in the upper 60s to near 70 Monday afternoon.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
VFR. Gusty winds out of the west-northwest will continue for a
few more hours before starting to diminish.

Extended Aviation Outlook: VFR through Thursday. Low chance of
MVFR Friday as low pressure passes offshore. VFR Saturday and
Sunday.

&&

.MARINE...
A dry cold front will quickly sweep east across the marine
zones late this afternoon into early this evening. Cold air
advection will spread across the relatively warm Atlantic waters
tonight. Forecast sounding over the Edisto buoy 41004 indicates
that the mixed layer will remain around 4kft deep through late
tonight, decreasing just below 3 kft by 12z. Wind gusts this
evening may frequently reach in the low 30 kts across the outer
GA waters. Near shore waters may see periods of gusts near 30
kts this evening, generally 10 NM or greater. Winds will weaken
slightly during the pre dawn hours, but will still remain with
the Small Craft Advisory range. Wave heights are forecast to
peak around midnight, heights ranging between 4-8ft across
AMZ374.

Wednesday through Saturday: High pressure will build towards
the waters Wednesday. A brief increase in the pressure gradient
will lead to elevated winds and building seas Wednesday night.
Small Craft Advisories may be needed for all of the waters at
this time. Thursday, the gradient decreases, allowing winds/seas
to trend downward. Friday, winds/seas will deteriorate as the
pressure gradient tightens along/near a cold front that pushes
over coastal waters by Friday night. Small Craft Advisories will
be possible for most of the coastal waters near and behind the
front Friday evening and night. High pressure should then build
over the waters Saturday with conditions that remain below Small
Craft Advisory levels.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...Lake Wind Advisory until 5 AM EST Wednesday for SCZ045.
MARINE...Small Craft Advisory until 10 AM EST Wednesday for AMZ350-352-
     354-374.
     Small Craft Advisory until 10 PM EST this evening for AMZ330.

&&

$$

NEAR TERM...BSH
SHORT TERM...MS
LONG TERM...DPB
AVIATION...BSH/MS
MARINE...NED/MS



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