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773
FXUS62 KCAE 230802
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
402 AM EDT Mon Sep 23 2024

.SYNOPSIS...
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High pressure building over the SE US will keep warm conditions
over the Southeast into the first half of the work week.
Multiple shortwaves crossing the region will bring chances for
precipitation through much of the week. Confidence remains on
the lower side in the forecast beyond midweek as there is still
uncertainty associated with the evolution of an upper trough
moving toward the region and the track of a likely developing
tropical system in the Gulf.
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&&

.NEAR TERM /THROUGH TONIGHT/...
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Key Message(s):

- Upper ridge persists with above normal temperatures
- Isolated afternoon convection this afternoon and evening

Morning satellite imagery showing a blanket of stratus clouds
that has developed across the northern Midlands and into much of
North Carolina, while the remainder of the forecast area
remains relatively cloud free. WV imagery showing the upper
ridge across the Gulf Coast states ridging northeastward through
the Carolinas into the Mid-Atlantic. Surface analysis reveals
high pressure centered over New England ridging into the Mid-
Atlantic with a weak backdoor boundary pushing into the Midlands
and Upstate SC with some 3hr pressure rises behind it over
western NC.

This boundary figures to be a possible focus for afternoon
convection today as weak shortwave energy rounds the periphery
of the upper ridge. Atmospheric moisture is slightly above
normal with PWAT values around 1.5 currently and expected to
rise to around 1.7 to 1.9 inches this afternoon and evening. The
combination of this moisture and upper energy with a
destabilizing atmosphere with CAPE values around 1500-2000 J/kg
should yield isolated to scattered showers and possible
thunderstorms this afternoon across the southern half of the
forecast area. Hi-res models show this scattered convection this
afternoon into evening with another area of convection
developing in the higher terrain of NC and the Piedmont around
00z and moving into the northern Midlands through late evening
associated with shortwave energy moving toward the region as an
upper trough deepens over the middle of the country. Will carry
chance pops through around 06z across the north with slight
chance elsewhere through the late night hours.

Temperatures today should continue to be very warm but not
quite as warm as yesterday with more cloud cover expected. The
northern Midlands should be cooler than the rest of the area due
to morning stratus limiting solar insolation for a few hours
initially this morning before breaking by early afternoon. The
delayed destabilization will also support lower pops up north
early this afternoon. High temperatures are expected to range
from the mid 80s north to the lower 90s in the CSRA and southern
Midlands. Overnight lows tonight will be limited by elevated
dewpoints in the low level moisture and convective debris clouds
and expect lows in the upper 60s to lower 70s.
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&&

.SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Key Message(s):

- Upper ridge continues to bring above average temps.
- Afternoon and evening precipitation is possible each day,
  mainly across the northern portions of the forecast area
  Tuesday and western third on Wednesday.
- The chances for a tropical system to develop in the Gulf
  continues to increase.

Upper ridging over the region is forecast to slide offshore
during this time while an upper trough over the Upper Midwest
digs south and eastward. Shortwaves riding around the ridge
bring chances for showers and possibly a thunderstorm Tuesday
afternoon, mainly north. As far as the trough goes, the latest
trends indicate a higher probability it transitions to a closed
low as it approaches from the west. However, there remains
disagreement on where the low closes off, some guidance shows
that it`ll close off more north closer to the Midwest while
others show it closes off more south near the mid to lower
Mississippi River Valley. An associated surface boundary is also
expected to form and approach the area, bringing chances for
more shower or thunderstorm activity in the western portions of
the forecast area on Wednesday. Temperatures are anticipated to
remain above average through the short term period.

The other feature of concern for later in the week is the
potential tropical development in the southern Gulf of Mexico.
Models are in pretty good agreement that something will form
Tuesday if it`s not already developed by Tuesday morning. In
fact, NHC has increased the 48 hour probability of development
to 70% and 7 day probability to 90%. This makes sense based on
the model agreement and current activity in the southern Gulf.
There also seems to be good agreement among the deterministic
and ensemble models that the system strengthens and moves
northward towards the Gulf coast states. Individual members of
the GFS and Euro ensembles start to spread apart a bit as it
nears the coast, indicating there remains uncertainty in where
the system tracks.
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&&

.LONG TERM /THURSDAY THROUGH SUNDAY/...
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Key Message(s):

- Likely tropical system continues to develop in the Gulf, but
  uncertainty remains in its track.
- Chances for precipitation increase toward the end of the week.

The GFS and Euro ensemble members continue to increase in
spread with the track of the likely tropical system as it moves
toward shore and after landfall. It appears the upper
trough/closed lower over the CONUS will play a big role in where
the tropical tracks. If the upper low develops farther south,
guidance suggest it will cause a Fujiwara effect and pull the
tropical system westward after coming onshore. However, if an
upper low develops further north or the trough remains more of
an open wave, guidance is suggesting a higher chance the it will
get swept up in the flow and head towards the Southeast region.
Impacts to our forecast area are dependent on the track of the
system and there is still plenty to be ironed out in the coming
days.

Regardless of the track of the tropical system, chances for
precipitation increase toward the latter part of the week due to
the tropical system and approaching frontal boundary.
Temperatures are also expected to moderate a bit towards the end
of the week.
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&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Generally VFR conditions expected through the forecast period
except at KAGS which may see usual mvfr/ifr visibilities
overnight near the river.

Lingering late evening showers are diminishing and have shifted
south of the terminals, with mostly clear skies at the terminals
expected through the remainder of the night. Near calm to light
and variable winds expected through sunrise and will support
the potential for a little ground fog at the normally
susceptible AGS TAF site, but no restrictions expected
elsewhere. Winds pick up from the south today around 5 to 7
knots after 15z with afternoon VFR cigs as cumulus clouds
develop with strong surface heating. Cannot rule out isolated
convection once again this afternoon at the terminals but
confidence in impacts and timing not high enough to warrant
including more than VCSH at this time.

EXTENDED AVIATION OUTLOOK...There are no significant concerns
for restrictions at this time.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
SC...None.
GA...None.

&&

$$