353
FXUS62 KCHS 122028
AFDCHS

Area Forecast Discussion
National Weather Service Charleston SC
428 PM EDT Mon Aug 12 2024

.SYNOPSIS...
A stationary front will remain just to the west through Tuesday
before dissipating. Weak high pressure will build in from the
north during the middle of the week and prevail into the latter
part of the week.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Afternoon into the evening: Thunderstorms are developing in the
anticipated area across the Tri-County and back to the
southwest where the area is situated between the front and the
sea breeze. Further inland, dew points are a bit lower, with
some upper 60s at a few observation sites. MLCAPE values are
between 1,500-2,500 J/kg with a stripe of DCAPE values on the
order of 1,000-1,200 J/kg. With DCAPE this high there will
continue to be a damaging wind threat, especially where updrafts
are enhanced near boundary interactions. Overall, the severe
threat isn`t particularly high but it isn`t out of the question
for there to be a Severe Thunderstorm Warning or two. Locally
heavy rainfall will also be a concern, especially since this
area is still feeling the effects of rainfall and flooding from
Debby.

Convection should steadily diminish through the evening hours
and we expect the bulk of the overnight to be dry. Lows are
forecast to reach the mid 70s in most areas, with upper 70s
along the coastal corridor. Some model guidance suggests there
could be some shallow ground fog but no significant visibility
reductions are expected.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: The region will be caught between a broad upper trough
over the mid Atlantic and Northeast states and a mid/upper
level ridge centered over the Gulf of Mexico. A surface trough
or weak backdoor front is expected to move southward toward the
area during the day. Given PWs just above 2 inches, the presence
of some upper forcing from an upper level short wave over North
Carolina, and the approaching surface trough/backdoor front,
all point toward above climo PoPs, especially for our SC zones.
Have capped PoPs in the high end chance/low end likely for now
over the northern 1/3 of the area, but they may need to be
raised. Models also show adequate deep layer shear of 35-45
knots, but instability limited due to warm mid levels. Thus,
there is only a small chance for isolated strong to severe
storms, especially within boundary interactions later in the
afternoon. Locally heavy rainfall possible, which could easily
cause ponding of water, especially in/around urbanized areas.
Highs ranging from around 90 northern 1/3 of the area to mid 90s
southern GA/Altamaha region. Convection should decrease in
coverage later Tuesday night, but kept slight chance/chance PoPs
through about midnight. Lows in the lower to mid 70s.

Wednesday and Thursday: The upper trough axis begins to shift
off the mid Atlantic coast, while a surface trough/backdoor
front continues to slowly push southward, likely reaching the
southern forecast area by late afternoon. The front is expected
to stall near or just south of our region later Wednesday and
Thursday. For Wednesday, lingering deep layer moisture and
instability, along with the potential for a weak upper shortwave
on the backside of the upper trough, will keep at least chance
PoPs for much/all of the area, especially GA zones. By Thursday,
a deep layer ridge is shown by models to build west and north
of the region, helping to push deep layer drier conditions
southward. This will translate to much lower PoPs. Have kept
slight chance for the extreme southern GA region, and below 15%
elsewhere. Would not be surprised if the entire area stays
convection free. Highs Wednesday in the upper 80s to around 90,
then mid to upper 80s Thursday, which would be a welcome few
degrees below normal if it verifies. As the drier air pushes
southward, this will help to lower our surface dewpoint
temperatures, especially by Thursday, where many will see
dewpoints in the mid to upper 60s, especially northern and
interior zones. These lower dewpoints will allow nighttime lows
to get cooler than they have been for a while, in the upper 60s
inland to the lower 70s coast Wednesday night.

&&

.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The deep layer ridge that was building from the west and
northwest in the near term is shown by global models to flatten
and push southward by later Thursday and early Friday and
another upper level trough builds into the Great Lakes Saturday,
then weakens as it moves into the northeast U.S. into Sunday.
Friday looks dry with PoPs below mention/15% as the deep layer
ridge hangs on for one more day. With more cyclonic upper level
flow Saturday and Sunday, along with increasing deep layer
moisture as the low level flow turns southerly, expect a return
to at least slight chance PoPs both days. Will continue to
monitor the potential for strong to severe storms this coming
weekend given the presence of a full latitude upper trough and
higher values of deep layer shear. High temperatures near to
slightly below normal Saturday, then a tad warmer by Sunday.

&&

.AVIATION /20Z MONDAY THROUGH SATURDAY/...
Isolated to scattered thunderstorms are possible this afternoon
and evening, with the best coverage expected to be around KCHS
where we have included VCTS from 1930-21z. Can`t rule out a
thunderstorm near KSAV or KJZI, but will handle those with
amendments as necessary. Overnight, there could be some shallow
ground fog around, but no reduced visibility expected at the TAF
sites.

Extended Aviation Outlook:

Tuesday: Some flight restrictions will be possible with
scattered afternoon and early evening convection, especially
KCHS and KJZI.

Wednesday: Additional brief flight restrictions possible at all
sites, mainly with afternoon/early evening convection.

Thursday and Friday: Less than 15% chance for convection, with
VFR expected to prevail as deep layer dry air tries to push
southward through the region.

&&

.MARINE...
This evening and tonight: Sea breeze flow along the land/sea
interface will persist into the evening mostly in the 10-15 knot
range though a few gusts up to 20 knots are possible.
Overnight, winds should be mostly southwesterly with speeds
diminishing into the 5-10 knot range. Seas should average 2-3
feet.

No highlights expected through the period. A weak surface
trough/backdoor front is expected to approach the waters late
Tuesday/Tuesday night, then move slowly southward, possibly
reaching the southern/GA waters Wednesday night remaining just
south of the waters through Friday before weakening. Southwest
winds 10 knots or less Tuesday and seas 2 to 3 feet, veering to
northeast from north to south beginning Tuesday night, with
northeast winds expected all waters by later Wednesday through
Friday. Winds Wednesday through Friday generally 10-15 knots
with some gusts near 20 knots possible, especially SC waters.
Seas building to 3 to 5 feet, possibly touching near 6 feet
beyond 20 nm offshore by Thursday and Friday. By Saturday, high
pressure builds briefly over the waters with lighter winds from
the south, but seas may still hang on at 3 to 5 feet.

&&

.CHS WATCHES/WARNINGS/ADVISORIES...
GA...Heat Advisory until 6 PM EDT this evening for GAZ116>119-
     137>141.
SC...Heat Advisory until 6 PM EDT this evening for SCZ047>049-051.
MARINE...None.

&&

$$

NEAR TERM...BSH
SHORT TERM...RFM
LONG TERM...RFM
AVIATION...BSH/RFM
MARINE...BSH/RFM