Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 171201
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
701 AM EST Tue Jan 17 2017

.SYNOPSIS...
Weak high pressure will move across the Coastal Plain today, moving
over the western Atlantic tonight. A front will then waver
across the area through early next week keeping conditions
unsettled.

&&

.NEAR TERM /THROUGH TONIGHT/...
Widespread dense fog and low stratus lingers across the
forecast area this morning. Forecast soundings indicate that a
llvl inversion persist inland through the mid morning hours.
Across the near coastal waters, high resolution guidance
indicates that a thin band of sea fog will persist through much
of the day and into tonight. I will update the forecast to
adjust timing and placement of fog this morning. In addition, I
will add a mention of sea fog across the near coast waters
through the daylight hours. Otherwise, the update will feature
slow warming during the early morning hours, followed by strong
rises with decreasing mid day sky cover. No changes made to the
dense fog products.

As of 220 AM: Sfc high pressure sourced from eastern VA/NC continued
to ridge SW across the Carolinas and GA. Recent 11u-3.9u satellite
product indicated the leading edge of stratus was building WSW
across middle GA. Forecast soundings and observation trends
indicated that dense fog and widespread stratus will remain
across the CWA through the early morning daylight hours. NAM12
shows that the weak sfc ridge will slide off the Carolina coast
by mid morning. Forecast soundings show mixing generally
initiating during the late morning hours. Sfc winds should turn
from the SW and low cloud bases should dissipate by mid day. The
sfc pattern through the afternoon will feature a cold front
over eastern TN and high pressure off shore, supporting SW
through the rest of the day. At the mid level, the axis of a L/W
ridge will pivot over the Southeast today, gradually flattening
tonight. Temperatures should see little rise early this
morning, limited by widespread stratus and fog. However, the
late day break down of the cloud cover, SW flow, and mild
thickness should result in steady warming through mid afternoon.
I will forecast high temperatures to range from the mid 70s
inland to the upper 60s along the coast. It is interesting to
see the HRRR and NAM maintaining sfc condensation pressure
deficits less that 5 mbs through today. I will forecast a thin
band of near shore stratus developing late this afternoon.

The weak cold front will struggle to push across the southern
Appalachians tonight. However, the forecast area will remain between
the front and western Atlantic high pressure, supporting llvl SW
flow. NAM12 indicates that winds will remain nearly parallel over
the cooler shelf waters. Guidance indicates that sfc winds will
shift from the SSE after midnight. Given this setup, sea fog and
stratus is expected to slide over the coastal counties late tonight.
I will bank on the timing and placement of the high resolution
guidance. Low temperatures are forecast range in the upper 50s.

&&

.SHORT TERM /WEDNESDAY THROUGH FRIDAY/...
A weakening cold front will approach Wednesday before pushing
through Wednesday night and then pushing back northward as a warm
front Thursday night. Although there could be a few showers with the
initial frontal passage Wednesday and Wednesday night the better
rain chances will come Thursday night into Friday as deeper moisture
and synoptic forcing move into the area. Some thunderstorms will
also be possible Thursday night into Friday, mainly in Georgia where
the best instability is expected, although severe weather is
unlikely. Temperatures will remain above normal through the period.

&&

.LONG TERM /FRIDAY NIGHT THROUGH MONDAY/...
A wave of low pressure is likely to push off the NC coast Friday
night dragging a weak cold front into the area. The front will then
stall out with rain chances increasing from the south as deeper
moisture associated with an upper shortwave moving through the
region. The front will continue to be a source of low-level
convergence as it shifts northward as a warm front Saturday night
into Sunday and with deeper moisture returning to the area along
with strong forcing ahead of a deep upper low moving through the TN
Valley rain chances will be high and there will be a risk of some
stronger storms Sunday as the low-level flow increases along with
instability. Pretty good model agreement that the best rain chances
will be done by daybreak Monday with the cold front slowly pushing
through Monday, with breezy conditions expected. It will take some
time for the large upper trough to shift offshore so the coldest
temperatures will be delayed until Tuesday, although only dropping
to near normal levels.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Widespread dense fog and VLIFR stratus lingers across the
terminals this morning. Forecast soundings indicate that a llvl
inversion persist through the mid morning hours. Visibility
should improve at both KCHS and KSAV to between 1SM to 2SM.
During the late morning to mid day period, mixing should develop
and fog should decrease to MVFR to LMVFR levels. Guidance
indicates that restrictive ceilings will dissipate between 18Z
to 19Z. Southwest winds should strengthen to 5 to 10kts.
Following persistence and latest guidance, I will add a mention
of MVFR fog redeveloping by 6z tonight at both terminals.

Extended Aviation Outlook: Brief flight restrictions possible
Wednesday morning and again Wednesday night into Thursday as a
cold front moves through. Better chance of restrictions expected
Friday as a warm front moves through.

&&

.MARINE...
Dense fog will continue to be highlighted with a Dense Fog Advisory
through 10 AM for all marine zones. Dense fog is expected to
gradually thin during the morning daylight hours. However, low
stratus may expand this afternoon. Light SW winds this morning
are forecast to increase to around 10 kts this afternoon, 10 to
15 kts for the MZ350. Seas should remain between 1 to 2 feet
within 20 nm, 2 to 3 feet across MZ374. Tonight, SSW winds will
continue over the GA and SC waters. Models indicate that sea fog
and stratus may gradually increase this evening and through the
overnight hours. It is possible that dense fog can redevelop
over the offshore waters and adjacent harbors this evening.

Wednesday through Sunday: No significant concerns regarding
winds/seas, although fog could reduce visibilities, especially over
the near shore waters, mainly into Wednesday night, Friday and again
Sunday. Conditions could near Advisory levels across the Charleston
County waters Wednesday and beyond 20 nm Friday and again later
Sunday.

&&

.CLIMATE...
Record highs for Tuesday, 17 January:
KCHS: 78/2013 and previous years
KCXM: 78/1928
KSAV: 81/1943

Record highs for Wednesday, 18 January:
KCHS: 77/1952
KCXM: 79/1928
KSAV: 81/1937

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Dense Fog Advisory until 10 AM EST this morning for GAZ087-088-
     099>101-114>119-137>141.
SC...Dense Fog Advisory until 10 AM EST this morning for SCZ040-
     042>045-047>052.
MARINE...Dense Fog Advisory until 10 AM EST this morning for AMZ330-350-
     352-354-374.

&&

$$
NEAR TERM...NED
SHORT TERM...RJB
LONG TERM...RJB
AVIATION...NED
MARINE...NED/RJB
CLIMATE...



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