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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

                            
000
FXUS62 KCHS 160852
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
452 AM EDT Sun Jun 16 2019

.SYNOPSIS...
Atlantic high pressure will prevail into Tuesday. An inland
surface trough will develop by mid week then persist over the
Southeast into next weekend. 

&&

.NEAR TERM /THROUGH TONIGHT/...
Early this morning: The return flow of moisture off the Atlantic
and higher dew points than the past couple of days, will 
generate areas of stratus and stratocumulus, as well as patchy
fog, especially inland. Temps will start the day considerably 
warmer than Friday and Saturday began.

For today: Flat ridging will prevail aloft, while surface and
low level high pressure extends from the Atlantic overhead, as 
a subtle lee side trough develops. There is still plenty of dry 
air in the H7-H3 layer, but with PWat climbing back closer to 
normal for mid June, the sea breeze may have something to work 
with to generate showers and t-storms. Since there is still a 
cap around H85-H7 and low level lapse rates aren't that 
impressive, we won't show anything more than 20% POP this 
afternoon, mainly across Georgia. Scattered to broken cumulus 
clouds will develop, leading to partly or mostly sunny skies 
throughout, and with H85 temps of 16-17C, max temps will warm 
into the upper 80s and lower 90s. 

Tonight: As the surface ridge axis positions itself south of the
area and within a southerly low level flow, it'll be an even
warmer night, with lows around 2-3F above climo. Marine-induced
showers will make a run for the coast, but with still quite a
bit of subsidence, we don't have any mention of rain over land.
There could be some fog overnight with favorable condensation
pressure deficits and the lack of mixing. But since it'll be a  
little tough to reach our cross-over temps, we have not included
it in the forecast at this time.

&&

.SHORT TERM /MONDAY THROUGH WEDNESDAY/...
Monday: Most of the day will still be under broad upper ridging 
although gradually deepening moisture will advect north across 
South GA. Temps should warm into the lower 90s inland during the
afternoon with isolated to scattered showers and tstms developing as 
the sea breezes pushes inland. We have POPs tapered from 20 percent 
Charleston area to 30-40 POPs inland GA where the higher 850 MB 
theta-e advection is noted after 18Z. 

Tuesday: The upper ridge will give way to a dampening mid level
short wave which is forecast to move from the Tennessee Valley 
region early in the day into GA and the Carolinas Tuesday night.
Over our area during the convection initiation hours of the 
afternoon, no real stand-out parameters or lifting mechanisms other 
than the typical sea breeze and mesoscale boundary are noted. We 
maintained chance POPs mostly in the 40 percent range inland from 
the coast. Another warm day on tap with temps once again lower 90s 
many areas.

Wednesday: Deep layered wind fields will increase as the Piedmont 
surface trough develops inland. Conditions appear to favor 
convection by afternoon and showers and tstms should translate
toward the coast but it is uncertain where any organization is 
possible given model discrepancies at this point. If upstream 
tstms develop, they could produce some severe weather as higher
DCAPE values are indicated across the CSRA/Midlands. We will
need more evidence before raising concerns for stronger storms.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
A fairly robust mid level short wave is progged to pass through the 
southeast states Thursday into early Friday. This appears to be the 
most significant period for a potential risk of organized convection 
as 700 MB flow increases greater than 30 kt over much of the area. 
Timing and convective mode look tricky and global models continue to 
show moderate to strong instability at times late week. It still 
remains quite uncertain how convection will play out at this 
juncture. On Friday, the surface trough will mostly move offshore 
and POPs range from slight chance northern SC zones to chance GA. 
Upper ridging is expected to build over the weekend with hot and 
humid weather and at least a slight chance for afternoon/evening 
showers and tstms. Temps on average will run above climo by several 
degrees for highs and lows through most of the medium range.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
Due to the higher dew points there could be a little ground fog
at KCHS and/or KSAV close to daybreak. 

Then for later today, isolated SHRA and/or TSRA will form on 
the sea breeze, but any direct impacts at either airfield are 
too minimal to address at this time. 

Extended Aviation Outlook: Mainly VFR. Brief flight restrictions are 
possible in afternoon showers/thunderstorms, especially by mid week.

&&

.MARINE...
Today: The Atlantic Ridge will be the dominate weather feature
as it stretches across the local waters. Sea breeze circulations
will back our S and SW winds of 5-10 kt this morning around to 
the SE and S as high as about 10 kt this afternoon. Seas will be 
no larger than 2 or 3 ft all day.

Tonight: The synoptic pattern holds under the influence of
Atlantic high pressure, producing S winds around 10 kt throughout,
with seas to hold in a fairly steady state at 2 or 3 ft.

Monday through Friday: Between high pressure centered offshore and a 
trough of low pressure developing inland, winds will veer to 
south/southwest and increase in speed during the upcoming week. 
Winds of 15-20 knots will become more common by mid week, especially 
with the afternoon sea breeze near the coast and during periods of 
nocturnal surging, and gusts to 25 knots cannot be ruled out, 
especially overnight around midweek. Seas of 1 to 3 ft through 
Tuesday will build to 3-5 ft mid to late week.

&&

.TIDES/COASTAL FLOODING...
With the upcoming full moon and onshore winds, minor coastal 
flooding is possible along parts of the southeast South Carolina
coast (mainly for downtown Charleston) with the high tide this 
evening.

&&

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

&&

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