841
FXUS62 KRAH 250738
AFDRAH

Area Forecast Discussion National Weather Service Raleigh NC 335 AM
EDT Wed Sep 24 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 335 AM Wednesday...

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 /05Z WEDNESDAY THROUGH SUNDAY/...
As of 115 AM Wednesday...

Heavy rain showers and thunderstorms will continue to move E-NE
through the area and will impact the northern terminals through 10z,
before lifting off to the north. Outside of convection, IFR to LIFR
stratus restrictions are expected through this morning, followed by
gradual lifting to VFR by 18z as drier air temporary spreads into
the area. Isolated to widely scattered showers and storms could
develop during the afternoon. However 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...
Flood Watch from 8 PM EDT this evening through Wednesday morning for
NCZ007>010-021>026-041.

&&

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