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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 212053
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
353 PM EST Thu Feb 21 2019

.SYNOPSIS...
A nearly stationary front to the north will drop into the area
on Friday before lifting back north as a warm front Saturday
afternoon. A cold front will then sweep through from the west
Sunday, followed by high pressure on Monday. A low pressure
system could affect the area during the middle of next week. 

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
A stationary front is forecasted to meander over the Charleston
Tri-County area or just to the north. Low level moisture south
of this front will keep dew points in the 60s. This moisture
combined with fairly light SE winds should set the stage for a
foggy night. Models are in very good agreement showing patches
of fog this evening, with areal coverage and lower visibilities
after midnight. If trends continue, Dense Fog Advisories will be
needed. Models show we may have some precipitation, initially
inland, then elsewhere during later in the evening. The
precipitation threat then moves further north towards daybreak.
QPF should generally be 0.1" or less. Temperatures should be in
the lower 60s.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/...
A stalled front will be positioned just north of the forecast area 
Friday morning. Through the day, the front is expected to slowly 
drop south as a wedge of high pressure extends down the east coast. 
This will set up for a tricky temperature forecast. Southeast 
Georgia counties will be within the warm sector for much of the day, 
and highs could again reach around 80/low 80s. Further north, 
temperatures will be dependent on the speed of the front moving 
through. Rain chances will cap out in the 20-30% range. Large scale 
forcing isn't impressive but with the front and ample low level 
moisture, light showers will be possible.

The wedge will hold strong Friday night, then the front is expected 
to lift back north on Saturday as a warm front. Models have been too 
quick in this progression recently, so it will be another difficult 
forecast day for temperatures. By Sunday, the forecast area will be 
solidly within the warm sector. A cold front is then forecast to 
sweep through mid-day. A quick shot of rain will accompany the 
front, however models indicate the precipitation will be in a 
weakening state as it moves through the area. Rainfall totals will 
be a quarter of an inch or less, with higher amounts expected across 
interior zones.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Dry high pressure will build over the area Sunday night through
Tuesday. Upper disturbances could affect the area Tuesday night
through Thursday though there are considerable model 
differences with respect to how much precipitation occurs.

&&

.AVIATION /21Z THURSDAY THROUGH TUESDAY/...
18Z TAFs
Areas of stratus/fog are hugging the coastal waters while
pockets of stratocumulus are over the land areas. CHS and SAV 
could bounce back and forth from VFR to MVFR due to ceilings 
for the next few hours. MVFR is expected to prevail for a few
hours this evening due to ceilings. Overnight, lots of low 
level moisture and light winds will allow fog to develop at 
both terminals. While the start time has some margin of error, 
IFR should prevail. Conditions should gradually improve after 
daybreak Friday.

Extended Aviation Outlook: Restrictions in low ceilings and/or 
reduced visibility likely Friday night through Sunday morning.

&&

.MARINE...
Tonight: Satellite imagery and webcams show areas of dense fog 
persisting along along the immediate coast. There may be some 
fluctuation's in visibility in the next few hours, or maybe 
areas where it completely clears out as we pass peak heating. 
However, conditions are expected to worsen this evening and 
overnight as southerly winds continue to usher a warm, moist 
airmass over the cooler shelf waters. The Dense Fog Advisories 
were extended through the night. We also issued one proactively 
for the Charleston Harbor starting this evening and lasting 
through the night. Winds should be no more than 10 kt while seas
range from 2-4 ft.

Friday through Tuesday: A backdoor cold front will drop south 
through the waters on Friday, turning the winds from the south to 
northeast. A pinched gradient in the Charleston county waters could 
result in marginal small craft advisory conditions Friday night. It 
looks like a fairly short window in this occurring, so have held off 
on issuing an advisory at this time. The front will then lift back 
north as a warm front later Saturday, bringing winds back to a 
south/southwest direction. Speeds will increase on Sunday ahead of a 
cold front, and more solid small craft advisory conditions are 
expected for portions of the waters. A bout of SCA seas is expected 
to develop Tuesday and persist into Wednesday or Thursday as long 
fetch northeast flow sets up.

Elevated dew points and southerly winds will continue to favor sea 
fog into Friday. Visibilities will gradually improve through the day 
as northeast flow develops, first beginning in the northern marine 
zones then moving south as the day progresses. The Marine Dense Fog 
Advisory end times follow this trend. Another round of sea fog is 
possible late Saturday into early Sunday prior to a cold frontal 
passage.

&&

.TIDES/COASTAL FLOODING...
It's not out of the question that we could reach Coastal Flood 
Advisory levels at Charleston Harbor with the high tide Friday 
evening. The 5.9 ft MLLW astronomical tide would only require a 
1.1 ft anomaly which is quite possible based on the latest 
forecast for 15-20 kt NE winds along the Charleston County 
coast.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Dense Fog Advisory from 7 PM this evening to 10 AM EST Friday 
     for AMZ330.
     Dense Fog Advisory until 1 PM EST Friday for AMZ352.
     Dense Fog Advisory until 10 AM EST Friday for AMZ350.
     Dense Fog Advisory until 4 PM EST Friday for AMZ354.

&&

$$
NEAR TERM...
SHORT TERM...
LONG TERM...JRL
AVIATION...
MARINE...
TIDES/COASTAL FLOODING...