Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 260550
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
150 AM EDT Fri Apr 26 2019

.SYNOPSIS...
High pressure will prevail through the evening. Low pressure
and a cold front will bring unsettled weather on Friday. High
pressure will then return for the weekend and prevail through
the first half of next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Early this morning: Current radar imagery shows a large area of
convection/MCS working its way across south Georgia and the
Florida panhandle. The northern edge of this area is on the
weakening trend and the bulk of the convection should remain to
our south more closely aligned with where there is instability
this early in the morning. Also the airmass across the forecast
area is still relatively dry with mesoanalysis supporting
precipitable water values in the 1-1.2 inch range. Showers will
likely begin to approach from the southwest over the next
several hours, but conditions suggest that these showers will
weaken and remain isolated to scattered at best. Overall,
conditions should be relatively quiet through sunrise.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH SUNDAY/...
Friday: An elongated trough from the western Great Lakes to
Florida at the start of the period will deepen and shift east. A
weak short wave embedded in the larger trough will be just
northeast of the area at start the day and this should result in
a tendency toward some sinking motion while drier air moves in
at the mid and upper levels. This combined with a strong signal
from the models that strong/significant convection will move
east across the northeast Gulf of Mexico and into Florida early
on Friday while more significant convection and lift moves from
northern Georgia into western North Carolina. Also, the timing
of front is not optimal to develop significant instability out
ahead of it and the model show just modest instability
developing mainly along the coast. Bottom line, it appears that
this split in the precipitation will result in a lower threat
for precipitation and for lighter precipitation amounts for our
CWA. Therefore have lowered rain chances to no more than 50
percent for Friday. With the dry mid levels, cannot rule out a
strong thunderstorm along the front with wind being the primary
threat, but at the present time am not sure how much
precipitation there will be with the front. The precipitation
should end from southwest to northeast rather quickly Friday
afternoon. Friday will be quite windy both ahead of the front
and behind it with some wind gusts up 30 to 35 mph possible.
Wind gusts on Lake Moultrie are close to Lake Wind Advisory
levels, but will defer to the overnight shift to make the final
call. Highs away from the coast will be in the lower 80s, with
generally 50s in the wake of the front Friday night.

Saturday and Sunday: Modest mid level west-northwest to west
flow aloft will prevail in the wake of the large scale trough
moving away from the area. Surface high pressure will build over
the area Saturday, then move offshore Saturday night and into
Sunday. Dry air and subsidence will result dry conditions and
little if any cloud cover. High temperatures will be near normal
Saturday and a several degrees above normal on Sunday.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Models are in good agreement showing high pressure over or
nearby our area during the long term, bringing dry conditions
and temperatures at or slightly above normal.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
A cold front will approach the region from the west through
sunrise and then cross the area by this afternoon. Showers and
possibly a thunderstorm could impact the terminals with the
frontal passage, but there remains considerable uncertainty
regarding the coverage and intensity of any showers/storms that
develop. Confidence is still low enough to only warrant a VCSH
mention at both sites, mainly in the morning. Winds will become
gusty out of the southwest this morning, then turn westerly this
afternoon and northwesterly this evening. Wind gusts into the
25-30 knot range will be frequent, especially at KCHS. There
could be a brief window of time for MVFR ceilings in the late
morning, but confidence is too low to go anything other than
prevailing VFR. Skies will clear out completely late this
afternoon and continue through the overnight.

Extended Aviation Outlook: VFR.

&&

.MARINE...
Rest of Tonight: Southerly winds will persist between Atlantic
high pressure centered well offshore and low pressure advancing
east over the Deep South. Winds have dropped a little near the
coast this evening, but still around 15 kts with some higher
gusts, especially Charleston Harbor and AMZ350. Withe the
pressure gradient expected to gradually tighten after midnight
as the cold front approaches from the west late, southerly winds
should remain elevated in the 15-20 kt range. Seas will build
to 3-4 ft across nearshore waters and 4-5 ft across offshore
Georgia waters. Still expect conditions will remain below Small
Craft Advisory levels through daybreak. A few showers or an
isolate thunderstorms could produce locally stronger wind gusts
toward sunrise.

Friday: Increasing surface pressure gradient ahead of an
approaching cold front and then a tight pressure gradient and
good mixing behind the front will result in elevated winds
Friday and Friday evening. Looks like frequent wind gusts of at
least 25 knots will occur in AMZ374 and AMZ330 during the
afternoon and evening hours as well as seas up to 6 feet. As a
result, have issued a Small Craft Advisory for these marine
areas from 16Z through 04Z. The winds are close for Charleston
Harbor and AMZ352 to be included, but have left them out for
now. Winds and seas will gradually subside Friday night.

Saturday through early next week: High pressure over or near
the area will dominate the forecast, bringing tranquil marine
conditions.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory from noon today to midnight EDT tonight
     for AMZ350-374.

&&

$$

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


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