-- Discussion containing changed information from previous version are highlighted. --
063
FXUS62 KRAH 251846
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
244 PM 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 THROUGH FRIDAY NIGHT/...
As of 235 PM Wednesday...

On Thursday morning, Hurricane Helene should be intensifying over
the Gulf of Mexico as it moves north, likely to make landfall along
the Florida Gulf Coast Thursday evening. Scattered showers and
isolated thunderstorms will continue Thursday morning along the
leftover boundary from today, slowly expanding to the east Thursday
afternoon. Have maintained likely pops across western counties
Thursday afternoon. As Helene weakens to a tropical storm by the
time it reaches northern Georgia Friday morning, rainfall will
expand farther across the forecast area Thursday night, with the
greatest coverage and intensity of rainfall likely to occur Thursday
night and Friday morning. 12Z models indicate that rain could come
to an end a little quicker than previously forecast as the dry slot
moves in from the south - likely pops will continue north of US-64
Friday afternoon, but pops should become more scattered across the
south in the afternoon, and all locations should be dry by late
Friday night.

While there is still spread as to the exact time of Helene once it
makes landfall, the overall trend across central North Carolina has
been a reduction in rainfall totals. A general one to two inches of
rainfall is expected, with greater amounts to the west. The maximum
wind gusts remain generally unchanged, ranging from 20-25 mph across
the east to 30-35 mph in the west. There have been some locations
that have received as much as five inches of rain in the last three
days. Considering how wet the ground is in some locations, despite
wind gusts that are expected to remain below tropical storm status,
there is the potential for many more trees to come down than would
be expected for the given wind speeds. The preceding rainfall will
also increase the risk for flash flooding and river flooding,
although there is not enough confidence in higher rainfall rates to
issue a flood watch. There will also be a risk for tornadoes on
Friday with ample moisture and instability for thunderstorms. This
threat will be evaluated more closely tonight and Thursday once
additional high-resolution model guidance is available.

High temperatures will range from the mid 70s in the northwest to
the mid 80s in the southeast. Low temperatures will range from the
upper 60s to the mid 70s Thursday night, then be in the mid to upper
60s Friday night as clouds clear out Friday night.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 244 PM Wednesday...

The mid-upper low/trough expected to pull Hurricane Helene northward
will linger over the TN Valley Saturday before slowly oozing
northeast through the Mid-Atlantic through early next week.

Saturday: The remnants of Helene will likely have moved over TN by
Saturday morning. The anomalous moisture associated with this system
will have congealed well to the north and west of central NC,
promoting a primarily dry day on Saturday. By Saturday evening,
however, some models suggest some of that anomalous moisture may
trickle back into our northwest Piedmont. As such, maintained a low-
end slight chance for showers Saturday afternoon and evening.
Otherwise, daytime highs in the lower to mid 80s is expected.

Sunday through Wednesday: As the mid-upper low slowly migrates
across the mid-Atlantic through early next week, additional daily
showers and thunderstorms will be possible.  Will maintain low
slight to chance PoPs each day for now, with highest chances across
the north where better moisture will pool and upper forcing for
ascent appears strongest.  There does seem to be good consensus that
the upper trough will shift offshore through Wednesday, behind which
nwly flow aloft will usher in drier air by mid-week (mean ensembles
suggest <1 inch PWAT may encompass our area by Thursday morning).

Temperature wise, we`ll generally see upper 70s to lower 80s through
Wednesday.  There is a signal for a potential cool down Wednesday
night into Thursday, but confidence is low at this point.
-- End Changed Discussion --

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 225 PM Wednesday...

Aviation conditions will be mostly favorable through this evening,
but lowering cigs and increasing rain chances, esp W, will bring
potential adverse conditions tonight. Pockets of MVFR cigs persist,
but overall, conditions have improved to VFR over much of the area.
Scattered showers are moving into southern sections currently,
likely to affect FAY with brief MVFR conditions prior to 20z, and
additional isolated to scattered showers and a few storms are
possible through this afternoon, with low predictability at any
given TAF site, although chances are best at INT/GSO/RDU. After 03z,
low cigs are expected to form, dropping to IFR/LIFR at INT/GSO/RDU
and MVFR at RWI/FAY, lasting through daybreak. A few showers are
likely at INT/GSO late tonight and through Thu morning, but
elsewhere, the best rain chances will hold off until after 16 Thu.
Surface winds will be under 12 kts, lightest between sunset and
sunrise, generally from the ESE or SE.

Looking beyond 18z Thu, what is now Hurricane Helene is expected to
make landfall in the central FL panhandle early Thu evening, then
track N and NNE through GA and into eastern and central TN Thu night
through early Fri afternoon. Moist flow ahead of and east of Helene
will bring predominantly adverse aviation conditions to much of
central NC Thu afternoon through early Fri morning, with periodic
rain bands bringing occasionally sub-VFR conditions in moderate to
heavy rain with isolated storms, along with frequent gusts over 20
kt. Low level wind shear may occur esp at FAY/INT/GSO early Fri
morning, but confidence is low. Conditions will improve to VFR from
S to N Fri, lasting through Sat. A chance of showers/storms will
return esp to the NW Sun into Mon. -GIH

&&

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

&&

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