516
FXUS62 KCAE 251051
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
651 AM EDT Wed Sep 25 2024

.SYNOPSIS...
Warm and mainly dry conditions are expected today as the region
remains under the influence of upper ridging to the east. Rain
chances increase tonight as tropical moisture is advected into
the forecast area. Tropical Storm Helene is forecast to become a
hurricane today as it moves north into the Gulf of Mexico. Confidence
in impacts from Helene Thursday into Friday across our area
continues to increase, but uncertainty remains in the exact
track and impacts of the system.

&&

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

- Areas of low clouds and patchy fog dissipate after daybreak.
- Partly to mostly cloudy and warm today.
- A few afternoon and evening showers or thunderstorms possible,
  mainly across the Western Midlands and CSRA.
- Rain chances increase tonight, especially in the west.

Early morning satellite imagery shows scattered clouds across
the forecast area with areas of low clouds and patchy fog
ongoing. The low clouds should lift quickly after daybreak.
Upper ridging will remain anchored off the eastern seaboard
today while an upper low sets up over Southern Illinois. This
will result in a southerly flow across the Southeastern US with
increasing PWATs across the forecast area. Having said that, it
appears that rain chances will be low through the daytime hours
for the majority of the forecast area. A few showers or
thunderstorms may develop, especially across the Western
Midlands and CSRA. It`ll be partly to mostly cloudy and warm
with forecast highs generally in the mid-80s.

Tropical Storm Helene, currently centered east of Cancun, is
forecast to be become a hurricane today and move north into the
GOMEX. Moisture will stream into the region ahead of the cyclone
resulting in an increase chance for rain tonight. Once again,
the highest probability of precipitation will be across our
western counties. The rain may be heavy at times towards
daybreak in parts of the the CSRA and far western Midlands. Low
temperatures will be in the lower 70s.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
Key Message(s):

- Impacts from Helene begin to affect the region Thursday.
- Heavy rain, nocturnal tornadoes, and gusty winds are the expected
  threats from Helene.
- Biggest impacts overnight Thursday into early Friday morning.

Confidence continues to increase that the area will be impacted
by Helene, but there remains some uncertainty in the track and
exact impacts. Continue to monitor the latest forecasts for
updates.

Helene is forecast to continue moving north northeastward,
likely making landfall in the big bend of Florida Thursday
evening, then passing just to our west Friday morning. Latest
guidance continues to indicate that it moves quickly north and
begins to phase with an upper low in the Lower Mississippi
Valley. These factors will likely aid in keeping Helene`s
structure fairly well in tact as it approaches the area, which
is unusual to have a tropical system remain in tact this far
inland from the Gulf. As Helene approaches and phases with the
upper low, it is forecast to bend northwestward. Impacts from
Helene are expected to move into the CSRA Thursday morning with
rainfall and continue north and westward through the day. The
biggest impacts are expected overnight Thursday into the pre-
dawn hours on Friday. With the fast movement, Helene should be
mostly out of our area by Friday evening. While the center of
Helene is forecast to pass to our west, we`ll still feel some
impacts.

Heavy rain:

Moisture from Helene will increase through the day on Thursday,
bringing PWATs to around 2.5 inches or greater. This will lead to
the heavy rain threat, especially overnight as the center nears the
forecast area. The heaviest rain threat is currently over the CSRA
into the western Midlands, with an even greater threat in the
Upstate. As with many tropical systems, a sharp rainfall gradient is
likely to set up, which looks to be along the I-26 corridor as of
the latest forecast. The location of the gradient is hard to pin
down at this point, so it could change. Total rainfall amounts range
roughly 2-5", with locally higher amounts possible. This could lead
to localized flash or urban flooding, especially in the CSRA.
However, don`t think a flash flood watch is warranted at this time
due to the isolated nature of the threat. With the heaviest rains
expected in the Upstate, eventually that water has to go through the
rivers in the days after Helene, so river flooding is becoming
increasingly likely.

Nocturnal tornadoes:

There is a high probability (80-90%) that we will be in the favored
northeast quadrant of Helene for tornadoes. Ensemble means for
surface based CAPE remain in the 250-500 J/kg, but some
deterministic model solutions are showing higher values than that.
Storm relative helicity are pretty high, especially given that is
during the pre-dawn hours. In general, storm helicity values max out
around 500-700 m2s2 with the different model solutions. Thus, the
tornado threat continues to increase for the early pre-dawn morning
on Friday, unfortunately. The greatest threat for tornadoes is along
and east of the I-20 corridor. Be sure to have multiple ways to
receive warnings!

Gusty winds:

As Helene approaches, models suggest 850 mb winds increase to 50+
knots, which will likely result in wind gusts in excess of 40 mph at
times. LREF and NBM continue to indicate a great than 80% chance of
such winds for most of the forecast area. I think the highest
likelihood of these winds will be in the western portions of the
forecast area, closer to the center. As with the other threats, the
main timing appears to be late Thursday/early Friday morning for the
strongest gusts.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
Key Message(s):

- Helene becomes absorbed by upper level low on Friday night and
  Saturday
- Cutoff low hangs around through early next week

Helene is expected to get absorbed by the upper low. Then the low
meanders around the area for a few days. As a result, daily chances
of precipitation continue for much of the period. Temperatures are
expected to be seasonal through the time period.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
Ceiling Restrictions Possible at the Terminals this Morning....

Low clouds and fog have quickly developed at CAE/CUB/OGB early
this morning resulting in LIFR ceilings. Low clouds and fog are
expected to persist during the next few hours. Light and
variable winds at daybreak turn south to southeast and may be
gusty at times this afternoon. The chance of rain remains low at
the terminals through this evening. Low clouds and rain will
move into the terminals tonight.

EXTENDED AVIATION OUTLOOK... Restrictions are possible Thursday
into Friday as Tropical Storm Helene passes west of the
forecast area. Low ceilings, heavy rainfall, and strong winds
are possible.

&&

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

&&

$$