061
FXUS62 KGSP 271217
AFDGSP

Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
817 AM EDT Fri Sep 27 2024

.SYNOPSIS...
Tropical Cyclone Helene will move quickly north through Georgia this
morning, bringing continued heavy rainfall, significant flooding and
strong winds to our area. After the storm departs this afternoon,
expect a calmer weekend with temperatures near seasonal normals.

&&

.NEAR TERM /THROUGH TONIGHT/...
***A HISTORIC RAINFALL EVENT IS UNDERWAY FOR THE SOUTHERN
APPALACHIANS AND VICINITY WITH WIDESPREAD/LOCALLY CATASTROPHIC FLASH
FLOODING EXPECTED***

As of 750 am: The track of Helene has been a bit east of the
forecast this morning, and the center is currently located near
Toccoa, GA. Based upon radar trends, the cyclone is beginning to jog
more to the N/NW, and the center will track quickly across far
southwest NC over the next couple of hours. The last band of
tropical rain is currently moving rapidly north through the Upstate,
with intense rainfall rates of 1-2" per hour noted. This band will
move over the Blue Ridge, including the Asheville/Hendersonville
area, where severe to catastrophic flash flooding is ongoing...
within the hour. Locations that are experiencing severe flooding
will likely see the situation become quickly catastrophic.
Otherwise, virtually the entire CWA is covered with Flash Flood
Warnings, and all but the northeast corner of the area is expected
to see some degree of flash flooding this morning before the rain
comes to a merciful end by noon in most locations.

Winds are gusting in the 40-55kt range across much of the CWA, and
have seen occasional gusts in the 60-65 kts range. This has resulted
in widespread downed trees and power outages across the area. Winds
will continue to howl for a couple of more hours before beginning to
taper down to something more sane during late morning/early
afternoon.

E/SE flow north of the cyclone has advected higher surface-based
buoyancy to the tune of 300-500+ J/kg into the southeast corner of
the CWA. Some of this may continue to be pulled north into the I-77
corridor, and could interact with the very strong shear and helicity
parameters to pose a threat of a brief spin-up. A Tornado Watch was
just issued for counties east of I-77...including Mecklenburg
County.

Helene will continue to advance quickly W=>NW of the forecast area
late this morning into the afternoon, with quickly improving weather
conditions as the column dries quickly. However, flooding on some
larger tributaries will linger into at least Saturday, while main
stem river flooding will linger into early next week.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 310 am Friday: Stacked low pressure over the TN/OH Valley will
steadily weaken while moving very little during the short term.
Spokes of vorticity passing south of the low center and brushing the
southern Appalachians will interact with elevated moisture and weak
instability to result in development of scattered, mainly diurnal
showers Saturday and Sunday...primarily over the mountains. Rainfall
rates/amounts will generally be tame, but can`t rule out some
locally heavy rainfall, especially on Saturday. Temperatures are
expected to be very close to normal through the weekend.

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
As of 300 am Friday: Upper low is forecast to be centered over the
Ohio Valley at the beginning of the extended, and is expected to
finally begin opening up and kicking into the Mid-Atlantic circa
Tuesday, as a strong short wave trough digs across the northern
Great Plains. This is expected to result in another round of mainly
diurnal showers on Monday. After that, it looks like we finally see
an end to precip chances for the remainder of the forecast period,
as drier air filters into the area in association with with
continental high pressure. Temperatures are expected to be slightly
above normal during the first half of the period, cooling a bit to
normal with the building surface high.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
At KCLT and elsewhere: Winds are gusting in the 40-55 kts range
across much of the Terminal Forecast Area this morning, as Tropical
Cyclone Helene is moving rapidly N/NW across the far western part of
the area. Directions will turn the dial quickly from E/SE to
southerly throughout the morning, and should begin to steadily
diminish after 15Z or so. Gusts will continue into the afternoon,
but should diminish to less than 30 kts by mid/late afternoon, with
gusts diminishing completely this evening. Strong LLWS as high as 70
kts will also continue through the morning. Otherwise, tropical
rains will end quickly this morning, and IFR cigs are expected to
fill in at most sites within 1-2 hours of precip ending. Cigs should
improve to MVFR during early afternoon and lift to VFR by mid/late
afternoon.

Outlook: Isolated to sct mainly diurnal/mainly mountain convection
(primarily showers) will be possible thru early next week. Morning
fog/low stratus will be possible each day, mainly in the mountain
valleys.

&&

.GSP WATCHES/WARNINGS/ADVISORIES...
GA...Flood Watch until 2 PM EDT this afternoon for GAZ010-017-018-
     026-028-029.
     Tropical Storm Warning for GAZ010-017-018-026-028-029.
NC...Flood Watch until 2 PM EDT this afternoon for NCZ033-035>037-
     048>053-056>059-062>065-068>072-082-501>510.
     Tropical Storm Warning for NCZ033-048>053-056-058-059-062>065-
     068>071-082-501>510.
     Wind Advisory until 2 PM EDT this afternoon for NCZ035>037-057-
     072.
SC...Flood Watch until 2 PM EDT this afternoon for SCZ008>014-019-
     101>109.
     Tropical Storm Warning for SCZ008>014-019-101>109.
&&

$$

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