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Area Forecast Discussion (AFD)

Issued by Charleston, SC (CHS)

FXUS62 KCHS 161633

Area Forecast Discussion
National Weather Service Charleston SC
1233 PM EDT Sun Jun 16 2019

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


Update: Radar imagery is showing showers developing in McIntosh
County along the sea breeze. This is a little earlier than what
we were initially thinking. Though, the synoptic models and the
CAMs are showing this, perhaps a little more so in the newest runs.
Additionally, SPC Mesoscale Analysis shows increasing
instability across our area, especially in our GA counties. With
this in mind, we did a quick update to expand the slight chance
POPs further north and inland for this afternoon.

Rest of 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. Dew points and PWATs are
gradually increasing across the area and with the afternoon sea
breeze, there should be enough to generate some
showers/thunderstorms this afternoon. The limiting factor to the
area coverage still appears to be a cap around H85-H7. Highs
will rise into the upper 80s and lower 90s ahead of the sea

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 will be some fog overnight with favorable condensation 
pressure deficits and the lack of mixing, and we have added
mention to the forecast.


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.


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.


This afternoon, isolated SHRA and/or TSRA will form on the sea 
breeze, but the chance of any direct impacts at either terminal 
is too minimal to include in the TAFs at this time. 
Additionally, patchy fog will develop late tonight, especially 
inland from the terminals. Again, no mention in the TAFs at this

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


Today: The Atlantic Ridge will be the dominate weather feature
as it stretches across the local waters. The sea breeze will
transition winds 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.


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