401
FXUS62 KGSP 261055
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
655 AM EDT Thu Sep 26 2024

.SYNOPSIS...
Tropical Cyclone Helene is forecast to make landfall over the
Florida Panhandle late today. The remnant circulation will move
quickly north through Georgia bringing continued heavy rainfall,
significant flooding and strong winds tonight into Friday morning.
Expect a calmer weekend with temperatures near seasonal normals.

&&

.NEAR TERM /THROUGH FRIDAY/...
As of 3:45 am Thursday: ***A MAJOR RAINFALL EVENT FOR THE SOUTHERN
APPALACHIANS AND VICINITY WITH THE POTENTIAL FOR WIDESPREAD TO
CATASTROPHIC FLASH FLOODING IS OCCURRING***

A wide band of moderate to heavy showers continues to stream north-
ward within a plume of deep tropical moisture to the east of a
stalled frontal bndy still over eastern TN. Thus, the Predecessor
Rain Event (PRE) continues with a handful of Flash Flood Warnings
having been issued since midnight. We have not seen much if any
lightning over our area over the past few hrs, but the I-77 corridor
still appears to have upwards of 500 J/kg of sfc-based CAPE and deep
layer shear of 30 to 40 kt. Thus, another brief tornado remains
possible going forward. Nonetheless, the flash flood threat contin-
ues to increase as the rain continues to fall, mainly over the
foothills and along/near the Blue Ridge Escarpment. Another broad
area of heavier rain is currently approaching our area from the
south within this moist conveyor belt. This rain will likely put
more streams into flood thru the early morning hrs.

Otherwise, no changes were made to the Tropical Storm Warning or
the Flood Watch with this fcst update. The latest CAMs are still
suggesting that a swath of stronger wind gusts will spread over
our area just after 00z Friday and continue thru the morning. They
should start weakening by the afternoon, but conditions will remain
gusty thru the evening. Otherwise, all signs point to a significant
tropical event across the western Carolinas and northeast Georgia.
Helene will be a large and fast-moving storm, so any additional
minor shifts in the storm track probably won`t change much at this
point. We still expect a rare and significant amount of rainfall
over much of our mountains and adjacent zones with damaging to
catastrophic flooding likely. In the past, once the rainfall gets
above roughly ten inches, we have seen numerous reports of land-
slides across the high terrain. If you live in these areas, it is
imperative that you take whatever precautions you can now, as the
flood/landslide threat will continue to increase today and tonight.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/...
As of 245 am EDT Wednesday: Calm weather will return to the CWA by
Friday night, as the center of Helen will be spinning down over the
western Ohio Valley...with only some spotty showers expected to
linger across the mountains. Winds will remain gusty Fri evening...
albeit well below any Wind Advisory criteria...but will gradually
diminish through the night. With upper low remaining virtually
stationary across the TN/OH Valley, spokes of vorticity lifting
south of the low will approach the southern Appalachians Saturday
into Saturday night. This is expected to induce scattered shower
development...with perhaps a thunderstorm or two...mainly Saturday
afternoon/evening. Can`t rule out some locally heavy rainfall within
any of this activity, but any precipitation should mostly be light.
Temperatures will be right around normal through the period.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
As of 200 am EDT Thursday: Global model guidance is not in the
greatest agreement regarding the details of the evolution in the
upper pattern. However, as a strong short wave trough dips into the
northern Great Plains, the general idea is that the upper low...
centered somewhere over the Ohio Valley at the start of the
extended...will begin to wobble across the Mid-Atlantic and evolve
into an open wave at some point early next week. Scattered, mainly
diurnal convection (primarily showers) will be possible across the
forecast area each day from Sunday through Tuesday...with chances
becoming increasingly confined to the mountains later in the period,
as the pattern transitions to more of a NW flow regime in the wake
of the departing trough. Although precip chances are in the
forecast for much of the period, any rainfall is expected to be
light. Temperatures are forecast to be very close to climo through
the period.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
At KCLT and elsewhere: Moderate to heavy showers now cover most
of the fcst area with most terminals reporting either MVFR or IFR
cigs and visby at this time. Unfortunately, the worst is yet to
come. We could see a few lightning strikes embedded in the heavier
showers thru the morning with cigs dropping to IFR across the area
as more upslope forcing arrives and the deeper tropical moisture
streams up from the south. Once there, terminals should stay down
in the LIFR/IFR range for the rest of the taf period. Expect fre-
quent heavier showers to move thru the area with winds becoming
gusty from the SE after daybreak. Winds and gusts will continue
to strengthen later tonight and into Friday.

Outlook: TC Helene will bring widespread low cigs, heavy rain,
strong winds, and low-lvl wind shear thru Friday morning before
moving out of the area late Friday into Saturday. Isolated to
sct mainly diurnal convection will be possible thru the weekend.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch through Friday afternoon for GAZ010-017-018-026-
     028-029.
     Tropical Storm Warning for GAZ010-017-018-026-028-029.
NC...Flood Watch through Friday afternoon for NCZ033-035-048>053-
     056-058-059-062>065-068-069-501>510.
     Tropical Storm Warning for NCZ033-048>053-056-058-059-062>065-
     068>071-082-501>510.
SC...Flood Watch through Friday afternoon for SCZ008-010>013-019-
     101>109.
     Tropical Storm Warning for SCZ008>014-019-101>109.
&&

$$

SYNOPSIS...JDL
NEAR TERM...JPT
SHORT TERM...JDL
LONG TERM...JDL
AVIATION...JPT