Area Forecast Discussion
Issued by NWS Charleston, SC

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FXUS62 KCHS 162106

Area Forecast Discussion
National Weather Service Charleston SC
406 PM EST Mon Jan 16 2017

High pressure will extend across the area through tonight. A
front will stall across the area on Wednesday, then lift north
as a warm front Thursday night. Another cold front will affect
the area on Sunday.


This Evening and Tonight: A light northeast sfc wind will help
maintain high pressure over land this evening before it gradually
retreats to the mid Atlantic late tonight. A defined line of
low clouds remains over northern parts of the Tri-County area
where high pressure is strongest within the cooler northeast
flow. As far as chances for precip, a weak coastal trough
offshore will gradually lift north, spawning a few showers that
drift onshore through early evening hours. However, rainfall
accumulation should be quite low with any shower. By sunset,
most precip activity should remain offshore.

The main issue for tonight will be fog potential. Latest guidance
supports veering winds to south late tonight, advecting low-lvl
moisture into the area. Some moisture could advect onshore in the
form of sea fog where webcams are already hinting at patchy dense
fog near the immediate coast at times. The general consensus is
that sea fog should remain near the ground as it becomes
trapped under an inversion. Over land, isentropic ascent and
increasing low-lvl moisture from the south should also support
stratus late, which could eventually build down and support
additional areas of fog. Given the setup, A Dense Fog Advisory
over parts of Southeast South Carolina and Southeast Georgia is
possible at some point. Chances appear greatest between midnight
and daybreak Monday. Overnight lows will be mild, in the
low/mid 50s over most locations.


A deep layered ridge will maintain warm and dry conditions on
Tuesday with high temps in the mid to upper 70s. A flattening
upper level flow and a weak shortwave pushing east will favor a
weak back door cold front sinking into the area on Wednesday.
Although mostly cloudy skies will result, the subsidence
resulting from the WNW low-level flow and limited moisture
advection should limit rain potential as the front moves in.
Pre-frontal compression and downslope flow will produce another
warm day in the mid 70s. Thursday should again be mostly dry and
fairly warm though weaker downslope flow will yield highs a few
degrees lower than Wednesday.


Medium range guidance agrees that the axis of long wave H5
ridge will ripple over the region on Thursday. However, the sfc
front is expected to slowly lift north as a weak warm front.
PoPs across the forecast area will remain limited to SCHC, with
values slowly lowering from south to north. High temperatures on
Thursday are forecast to favor values around 70 degrees over

Thursday night into Friday, a negatively tilted H5 trough is will
pass over the southern Appalachians, brushing the CWA with weak
omega by sunrise Fri. The combination of deep moisture, weak
instability, and weak forcing should support sct showers. In the
wake of the front, dry air will spread across the region Sat am.

Saturday night into Sunday, a large low pressure system will
organize over the Great Plains, tracking over the Mid West by Sunday
evening. Moist SW flow will gradually increase across the forecast
through the late weekend. In fact, moist and warm llvl flow may
develop a band of sfc based CAPE as high as 1000 J/kg on Sunday. I
will increase PoPs to likely, for showers and thunderstorms. The
center of the H5 low is expected to pass over the mid Atlantic
region, with wrap around moisture crossing the CWA. SCHC showers and
near normal highs expected on Monday.


KCHS: IFR/MVFR conditions are likely for the next couple hours until
low clouds shift just north of the terminal. A period of VFR conditions
could prevail between 22-24Z before conditions lower to MVFR
shortly after sunset. IFR conditions will likely return overnight
due to fog or low stratus. Lowest cigs/vsbys should occur after
midnight into daybreak Monday morning. Conditions will likely
improve to VFR around 16Z Monday.

KSAV: VFR conditions are likely through early tonight. MVFR to
IFR conditions are then likely after midnight tonight and into
daybreak Monday morning as low stratus and/or fog develops over
the region. VFR conditions should then return around 16Z Monday.

Extended Aviation Outlook: Low clouds or fog could affect either
terminal Tuesday night. Brief flight restrictions possible
Thursday night into Friday with showers along a cold front.
A large low pressure system is expected to bring showers and
thunderstorms across the region Sunday through Sunday night.


This Evening and Tonight: Latest webcams show some patchy fog (some
dense) redeveloping near the Southeast South Carolina coast. The
general consensus is that fog could become more widespread later
tonight, especially over nearshore Georgia waters as sfc winds veer
from northeast to south late. Given the setup along with winds
remaining at or below 10 kts across most waters, Dense Fog Advisories
could be needed late. Otherwise, stable conditions will persist
in the marine layer. Seas will be no higher than 1-3 ft.

Fairly quiet marine conditions expected with regard to winds/seas
through Friday as a series of weak fronts affect the waters.
However, sea fog may persist through Wednesday afternoon as weak
onshore flow maintains moist air over the cool shelf waters.
Marine Dense Fog Advisories are possible at times, especially
late afternoon through mid-morning hours.


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




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