Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 202325

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

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.


Early this evening: Quick update for hourly parameters. No
changes needed to the going forecast.

High pressure will extend across the region tonight. An ill-
defined coastal trough could develop off the Georgia and far
northeast Florida coast late tonight as the surface ridge axis
shifts offshore, but models are trending weaker with this
feature. This seems reasonable given the expected orientation of
the surface high. Not impacts are expected. Could see some
shallow ground fog develop across areas closer to the Altamaha
River early Tuesday, but guidance has continued to back off on
its development likely due to increased cirrus over the area.
Maintained patchy fog in the Ludowici-Hinesville-Darien
corridor, but expect vsbys no lower than 4-5 miles. Lows will
range from the upper 40s across northern portions of Dorchester
and Berkeley Counties away from the Santee-Cooper Lakes to the
upper 50s along the Georgia coast.


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.


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.


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.


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


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.





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