Area Forecast Discussion
Issued by NWS Charleston, SC

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS62 KCHS 170613
AFDCHS

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

.SYNOPSIS...
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.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
As of 1 AM: Weak surface ridging has spread across the FA from the NE
tonight. IR satellite indicated a large shield of stratus
spreading SW across SC and GA, with large patches of mid and
high clouds across eastern SC. Guidance is in good agreement
with the widespread development of fog and low clouds through
the rest of the night. I will update the forecast to adjust
placement and visibility associated with the fog. No changes
made to the Marine Dense Fog Advisory.

Late this evening: No change to the going forecast. The latest
runs of the HRRR and RAP have been consistent showing fog expand
after midnight across the entire forecast area. To some degree,
this appears to be already be underway. Areas along the coast
are seeing at least periodic low ceilings and visibilities
moving onshore associated with sea fog over the coastal waters.
Meanwhile, locations across the Midlands are beginning to
experience fog (some dense). So, it will likely be some
combination of advection sea fog and inland radiation fog. Dense
fog advisories remain a distinct possibility depending on how
the fog evolves overnight.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH THURSDAY/...
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.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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
land.

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.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
Weak surface ridging has spread across the FA from the NE
tonight. IR satellite indicated a large shield of stratus
spreading SW across SC and GA, with large patches of mid and
high clouds across eastern SC. Guidance is in good agreement
with LIFR to VLIFR across the terminals through this morning,
especially at KSAV. KSAV observation and area Web cams indicate
that dense fog has developed over the lower Savannah River
Valley. KCHS has not seen restrictive conditions as of 530Z.
Based on LAV and CONSSHORT, expect MVFR vis and ceilings to
develop by 9z. During the pre dawn hours, I will TEMPO 1/2SM FG
with OVC002. Diurnal mixing should result in light SW winds by
mid morning with SCT to BKN MVFR clouds possible, dissipating by
mid day.

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.

&&

.MARINE...
Tonight: Recent calls to the Tybee Island Coast Guard and
Savannah Pilot Office dispatch, combined with satellite imagery
and photos from 41008 reveal that dense sea fog has developed
across the Georgia waters out to about 40 nm offshore. A dense
fog advisory has been issued for all of the Georgia waters and
the southern South Carolina waters through sunrise. The fog is
then forecast to spread across the remainder of the South
Carolina waters and the Charleston Harbor after midnight as the
low level flow weakens and begins to veer to more southerly.
The dense fog advisory may need to be expanded later tonight. 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.

&&

.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...None.
SC...None.
MARINE...Dense Fog Advisory until 8 AM EST this morning for AMZ352-354-
     374.

&&

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



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.