843
FXUS62 KRAH 251518
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1120 AM EDT Wed Sep 25 2024

.SYNOPSIS...
Mid-level disturbances, in moist, southwesterly flow aloft, will
interact with a stalled surface front that will weaken over the
Carolinas and VA through mid-week. Tropical Cyclone Helene is
forecast to make landfall in the Florida Big Bend late Thursday,
then move quickly north, while weakening, through the southern
Appalachians and OH Valley Friday and Friday night.

&&

.NEAR TERM /TODAY AND TONIGHT/...
As of 1120 AM Wednesday...

Just minor forecast changes this morning. With the late-night /
early-morning showers and storms having now pushed well to our
north, the daybreak stratus is now evolving into streams of agitated
cu as heating has pushed our SBCAPE to 1500-2500 J/kg thus far. With
a SSE low level flow and 30-40 kt of effective bulk shear,
development of isolated to scattered showers and storms is still
expected. But the presence of some fairly deep dry air noted on WV
imagery over all but our far NW will limit convective coverage, and
will maintain lower chance pops, restricting higher pops to the
Triad region and points NW. Temps are on pace to reach forecast
highs in the low-mid 80s, so minimal changes there. -GIH

Earlier discussion from 335 AM: Tropical Cyclone Helene is forecast
to intensify as a hurricane as it begins to move north-northeastward
across the eastern Gulf of Mexico. Deep southerly flow between a
mid/upper-level low that will eventually cut-off over the lower MS
and an upper level anticyclone over the western Atlantic will direct
the deep fetch of tropical moisture north and set up a predecessor
heavy rainfall event(PRE) over the spine of the Appalachians this
evening and tonight. Across central NC, we`ll see a brief reprieve
from the anomalous moisture, as drier air off the SE coast spreads
west into the area.

The ongoing area of heavy showers and storms over the northern
Piedmont and northern coastal plain counties will lift north into VA
through daybreak as the weak sfc boundary lifts north and drier
spreads from the SE, ending the flooding rain threat. After a late
morning/mid day lull in precip/rain, isolated to scattered weak
convection will develop during the afternoon, with the best coverage
expected across the western Piedmont. While scattered rain showers
could linger across the far western zones overnight, the remainder
of the forecast area should stay mostly dry.

We`ll still have widespread cloudiness, with morning stratus lifting
throughout the day. Slightly warmer with highs ranging from near 80
north t o mid 80s south. Lows 65-70.


&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 335 AM Wednesday...

...Minor impacts from Helene Arrive late Thursday/Thursday night...

Based on NHC`s official forecast, Helene will make landfall in the
vicinity of the Florida Big Bend Thursday evening. As Helene begins
to interact with the aforementioned cut-off low over the lower MS
Valley, the system will accelerate northward across Georgia and into
the southern Appalachians Thursday night/early Friday morning.
Moisture transport feed will get re-established into central NC by
the afternoon and into the night, with PwATs increasing 2.25-2.50"
across the area.

Rain chances will gradually increase from west to east throughout
the day and into the evening with widespread light rain expected
area-wide during the overnight hours. Rainfall amounts are expected
to range from 1-2 inches across the far western Piedmont to 0.1-0.2"
across the coastal plain. Given the light rainfall rates, the
flooding risk Thursday night looks relatively low, with a reasonable
worst case scenario of minor flooding in flood prone areas over the
far western Piedmont, including the Triad. It will become breezy
late Thursday evening into Thursday night with easterly gusts of 15
to 25 mph, strongest across western Piedmont and western Sandhills.

Highs Thursday ranging from mid 70s NW to lower/mid 80s south. Lows
in the upper 60s to lower 70s.


&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 320 AM Wednesday...

The latest NHC forecast takes the center of what is now Tropical
Storm Helene north into the Big Bend of FL as a major hurricane on
Thursday evening. It should then quickly weaken as it lifts north to
near Atlanta by Friday morning, then NW and eventually W into the TN
Valley late Friday into Saturday as it gets absorbed by a cutoff
mid/upper low. While the heaviest rain looks to be over the
mountains of western NC, Helene will be a large system, and the
latest rainfall forecast still has a total of 2 to 3 inches across
the far western Piedmont, decreasing to around an inch in the
Coastal Plain. This includes an additional half inch to an inch
after 12z Friday. This much rain falling on top of already wet
ground may result in some flash flooding and river flooding. It
should also be noted that there is still a decent spread in ensemble
guidance on Helene`s exact track by the time it gets this far north,
which will affect how much rain we ultimately receive. The
widespread heavy rain should be largely over by Friday afternoon as
a dryslot moves in from the south, but with dew points in the lower-
to-mid-70s, there should be enough boundary-layer moisture and
instability to support some lingering scattered showers and storms
(mainly north). Low and mid level flow will be strong, and we will
be on the east side of Helene`s remnants, so a few strong to severe
storms and even an isolated tornado can`t be ruled out on Friday
afternoon and evening. Outside of storms, no tropical storm force
winds are expected, but 25 to 35 mph gusts will still be possible
through the day Friday especially south and west. With saturated
soils, it won`t take very strong winds to bring down some trees and
cause scattered power outages, as we also saw during Debby in
August. High temperatures on Friday will be in the upper-70s to
lower-80s, with lows Friday night in the mid-60s to lower-70s.

After a brief mostly dry period from Friday night into Saturday,
tropical moisture associated with Helene`s remnants to our west will
spread back into the area. There is a large amount of spread in
ensemble guidance on where the low tracks. But regardless of the
exact track, isolated to scattered showers and storms will again be
possible on Sunday and especially early next week (maximized each
afternoon and evening), when the latest deterministic guidance moves
the system back east through the Mid-Atlantic as it opens up into a
trough. The warmest day will be Saturday with mostly sunny skies, as
forecast highs are in the lower-to-mid-80s. Highs then cool back to
below normal by early next week as clouds and precipitation
increase, but lows stay above normal (generally 60s).

&&

.AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
As of 645 AM Wednesday...

Heavy rain showers and thunderstorms are exiting north of the area.
The widespread MVFR to LIFR stratus restrictions will gradually lift
to VFR from south to north from 15-19z as drier air temporary
spreads into the area. Isolated to widely scattered showers and
storms could develop during the afternoon. Due to expected limited
coverage, will not include any mention at this time.

Widespread IFR to LIFR restrictions are expected to re-develop area-
wide tonight, with the lowest restrictions expected at KINT and KGSO
and KRDU.

Outlook: Under a persistent anomalous moisture regime, late
night/early morning sub-VFR ceilings and visibilities will be
possible each day in the outlook period. Additional showers and
storms will also be possible each day. While there is still some
uncertainty wrt to the evolution of Tropical Storm Helene, it does
appear that heavy rain and perhaps gusty winds will be possible late
Thursday night through Friday afternoon/evening, with greatest
impacts expected at KINT/KGSO.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...MWS/CBL
NEAR TERM...Hartfield/CBL
SHORT TERM...CBL
LONG TERM...Danco
AVIATION...CBl/Luchetti