394 
FXUS62 KCHS 130823
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
423 AM EDT Wed Jun 13 2018

.SYNOPSIS...
A stationary front will dissipate across the region today while
a trough prevails inland through Thursday. A southward moving 
cold front will slowly move through the area Friday and 
Saturday, dissipating south of our area early next week. 

&&

.NEAR TERM /THROUGH TONIGHT/...
Today: The forecast area will remain within a baggy mid/upper 
level trough in the weakness between the ridge near the Four 
Corners region and the ridge over the Atlantic. At the surface, 
a weak stationary front will remain near the area, meandering 
around along the coast and dissipating through the afternoon. 
Early morning convection looks as though it will be mainly 
confined to the Charleston County coast, and any lingering 
boundaries produced by this convection should be enough to keep 
this area as the focus through the mid to late morning hours. 
Then as we transition to the afternoon, the focus for convection
is expected to shift further to the west and into southeast 
Georgia. Rain chances increase into the 50-60 percent range 
during this time and the convection is expected to shift to the 
east and southeast with time, such that by the evening hours the
best chances will be along and south of I-16. Storm motions 
will be quite slow (less than 10 knots), with precipitable water
values in excess of 2 inches. This means locally heavy rainfall
will be the main concern for today with almost no severe threat
due to the very weak flow through the depth of the atmosphere. 
High temperatures are expected to reach into the upper 80s for 
most areas, though hourly temperatures could fluctuate 
significantly depending on where showers and thunderstorms 
occur.

Tonight: An upstream cold front will begin moving into the 
Tennessee Valley and the southern Appalachians, which will 
promote a more uniform southwesterly flow across the forecast 
area. Evening convection should be mainly confined to southeast 
Georgia and should dissipate by the late evening. Overnight, the
best rain chances are expected to be over the coastal waters 
with isolated showers and storms possible right along the coast.
Overnight lows will only fall into the low 70s. There could 
again be some patchy shallow ground fog, but not enough coverage
is expected for inclusion in the forecast.

&&

.SHORT TERM /THURSDAY THROUGH SATURDAY/...
The mid-levels will consist of a weak trough over the Southeast
Thursday. Friday the trough begins to shift offshore while a 
strong ridge builds in from the west. By Saturday the trough 
axis is off the East Coast while the strong ridge stretches from
the Gulf of Mexico northward into the Great Lakes Region. At 
the surface, an inland trough will prevail Thursday with high 
pressure far in the Atlantic. A cold front will approach from 
the north Friday. The front will slowly move southward through 
our area Friday night into Saturday, eventually becoming located
just south of our area late Saturday. The synoptic pattern 
keeps ushering plenty of moisture into our area through 
Saturday. PWATs are expected to remain ~2". Though, their are 
indications they can pool up to 2.25" just ahead of the 
southward moving front. We have chance POPs Thursday, highest 
during the afternoon and along the sea breeze. POPs Friday and 
Saturday are highly dependent on the location of the front. We 
raised them to likely on Friday to account for the increased 
lift with the approaching front, but kept them capped at high 
end chance on Saturday. Though, POPs both days may still be too 
low. Another factor is the instability and how much is in place 
with ahead of the front. The models seem to be mixed on how much
will be in place Friday, with lower amounts on Saturday. These 
details will need to be refined further with upcoming forecasts,
including severe potential. The main threat now appears to be 
heavy rainfall and locally gusty winds. Nothing significant to 
note with the temperatures as daytime highs remain near normal 
and nighttime lows hover a few degrees above normal.

&&

.LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/...
A cold front is forecasted to be over or just south of our 
forecast area Saturday night, bringing unsettled weather to 
portions of GA. This slow moving front is expected to keep 
moving south Sunday and dissipate, pushed by high pressure 
centered off the coast of the Outer Banks. In the wake of this 
front will be a lower risk of thunderstorms and slightly cooler 
temperatures Sunday. On Monday and into Tuesday the high is 
forecasted to move further offshore, allowing a trough to 
develop inland. This will allow both temperatures and the 
thunderstorm potential to increase both of these days.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
The biggest concern through the next 6 hours is the potential 
for stratus at both sites. KCHS has already had some IFR stratus
and surrounding observations show that it is still out there. 
Therefore, will go with TEMPO IFR for a few hours and then 
prevailing IFR by close to sunrise. At KSAV it will likely take 
a bit longer for stratus to develop, but have introduced it 
there in a TEMPO at 10z. 

Stratus should scatter out and lift by 13z at both sites. 
Attention then turns to thunderstorm potential. Current thinking
is that KCHS will see the best chances in the 14-18z time 
period and 19-23z at KSAV. Kept TSRA MVFR for now but if direct 
impacts do occur, brief IFR periods of IFR will be possible.

Extended Aviation Outlook: Mainly VFR. Brief flight 
restrictions are possible in showers and/or thunderstorms, 
mainly each afternoon and early evening through Saturday.

&&

.MARINE...
Today: A weak stationary front is expected to dissipate across 
the region, with modest southwest flow in the 10-15 knot range 
expected by the afternoon hours. Seas are expected to be in the 
2-3 foot range. The main concern for the coastal water will be 
in the morning when light winds and very moist conditions could 
combine to create a favorable environment for water spouts. My 
midday the water spout risk should be significantly reduced. 

Tonight: Expect southwest winds mainly in the 10-15 knot range,
with some brief periods where speeds could increase a bit. Seas
will tick upwards and average 2-4 feet.

Extended Marine: Thursday the waters will remain between an 
inland trough and high pressure in the Atlantic. This synoptic 
flow will allow southwest winds to prevail. The exception will 
be during the afternoon near the coast where winds will likely 
turn south and increase a bit due to the sea breeze. A southward
moving cold front will slowly move through the area Friday into
the weekend. Winds will transition this weekend with the front,
but they will not increase to the point that we would need 
advisories. The front will dissipate south of our area early 
next week. Occasional thunderstorms could bring gusty/erratic 
winds and frequent lightning, especially during the overnight 
hours through Saturday.

&&

.TIDES/COASTAL FLOODING...
The approaching new moon and perigee could produce shallow 
coastal flooding with the evening high tide. A Coastal Flood 
Advisory could be needed. 

The combination of the new moon and occasional onshore winds 
should allow the evening high tides Thursday, Friday, and maybe 
Saturday to reach coastal flood advisory levels. Any heavy rain 
near the times of these high tides will increase the risk of 
flooding.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...None.

&&

$$

NEAR TERM...BSH
SHORT TERM...MS
LONG TERM...MS
AVIATION...BSH/MS
MARINE...BSH/MS
TIDES/COASTAL FLOODING...