Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 210241
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
941 PM EST Mon Feb 20 2017

.SYNOPSIS...
High pressure will linger across the region through the rest of this
week. A low pressure system will pass by just to the south Wednesday
into Thursday. A cold front will sweep across the region on Saturday
followed by Canadian high pressure.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Late this evening: No significant change to the overall
forecast. The high amplitude upper ridge axis will steadily
shift eastward across the region through the night. Plentiful
high clouds will stream through the flow originating from the
upper low closing over near the Arklatex. High pressure will
continue to ridge down the eastern seaboard, helping to drive a
light east to northeast flow. The forecast is dry thanks to
significant amounts of dry air in the low and mid levels. The
main thing to watch will be the potential for fog along and
south of the Altamaha to potentially sneak across the river and
impact locations across portions of southeast Georgia. Model
guidance looks similar to 24 hours ago and we did see some
patchy fog along the river this morning. The increase in high
clouds doesn`t exactly favor more fog, but given that is where
the best moisture will be, we have maintained the mention of
patchy fog. Lows are expected to be in the 50-53 degree range
for most areas, with some upper 40s further north especially in
the Francis Marion.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Deep layered ridging will maintain dry conditions and warm
temperatures on Tuesday despite increasing high cloudiness.
Deeper moisture advects into the region Tuesday night and
Wednesday as a powerful upper low drops southeast from the
central Gulf coast to southern Florida by Thursday. Weak surface
high pressure will persist over the area despite the center
shifting farther to the east. Given decreasing heights aloft and
broad south to southeast flow overspreading the area above the
surface, weak moist isentropic ascent will occur late Tuesday
into midday Thursday. This will yield isolated to scattered
showers from time to time, with potentially greatest coverage
over southeast GA closer to the upper low. Highs will be
slightly cooler on Wednesday, before warming back into the upper
70s Thursday.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
On Friday, south winds will strengthen across the CWA as a cold
front pushes east across MS/AL/TN. GFS indicates that H85 temps
will warm above 13C by late Fri afternoon. Guidance indicates
that high temperatures will reach the upper 70s near the coast
to the low 80s inland. The high temperatures may challenge record
values. Building instability should yield iso showers/tstms. The
cold front is expected to be west of the region by daybreak
Saturday. Min temps are forecast to remain very mild, with low
60s common Sat AM. GFS shows the passage of the sfc cold front
during the daylight hours on Saturday. CAPE values may range
from 1000-1500 J/kg, especially across the SC zones. Given the
timing and instability, it appears that the environment may
yield a band of prefrontal deep convection.

Dry Canadian high pressure is expected to build over the region
Saturday night and Sunday. Cooling thicknesses will yield lower
temperatures, but still remaining around 5 degrees above normal.
Moisture will rapidly stream northward ahead of a dynamic low
pressure centered over the Midwest. Strengthening return flow
will likely advect deep moisture and weak instability across the
forecast area on Monday.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
VFR through 00z Wednesday. Could see some shallow ground fog,
mainly southwest of KSAV, so no visibility reductions expected
at the terminal.

Extended Aviation Outlook: Patchy fog possible each morning
through Friday.

&&

.MARINE...
Tonight: Northeast to east flow will persist across the waters
tonight as high pressure gradually shifts off the coast. Winds
will be <10 kt this evening, then increase overnight in response
to a tightening pressure gradient. Seas will average 1-2 ft
across the waters.

Tuesday through Saturday: Persistent east to northeast flow
expected Tuesday through Friday as surface low pressure slowly
moves through northern FL and into the west Atlantic. No flags
expected through midday Thursday, though seas expected to
gradually build. We could see Small Craft Advisory seas over the
offshore GA waters by late Thursday.

Cold air advection should occur Saturday night into early Sunday,
likely resulting in gusty conditions. Wave heights are forecast
to build over 5 feet beyond 10 NM to 6-7 feet beyond 20 NM on
Sunday.

&&

.CLIMATE...
Record Highs for Feb 24:
KCHS: 81 set in 2012/1996.
KCXM: 81 set in 1930.
KSAV: 86 set in 2012.

Record Highs for Feb 25:
KCHS: 80 set in 1949.
KCXM: 80 set in 1930.
KSAV: 82 set in 1985/1930.

Record High Minimums for Feb 24:
KCHS: 60 set in 1992.
KCXM: 61 set in 1901.
KSAV: 64 set in 1980.

Record High Minimums for Feb 25:
KCHS: 62 set in 1992.
KCXM: 59 set in 2011.
KSAV: 63 set in 1992.

&&

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

&&

$$

NEAR TERM...BSH
SHORT TERM...JRL
LONG TERM...NED
AVIATION...BSH/JRL
MARINE...ST/JRL
CLIMATE...



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