683
FXUS62 KRAH 270725
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
325 AM EDT Fri Sep 27 2024

.SYNOPSIS...
What is now Hurricane Helene, centered near the Florida Georgia
border, will weaken gradually as it races northward through Georgia
tonight through early Friday morning. The storm will then slow down
and weaken further to a depression as it moves northwestward over
Tennessee into southwest Kentucky through Saturday.

&&

.NEAR TERM /TONIGHT THROUGH FRIDAY/...
As of 908 PM Thursday...

Tornado Watch for the southern tier of counties through 700 AM.

SPC has coordinated a Tornado Watch and the northern end of the
watch touches our southern tier of counties. The activity that may
become tornadic is expected to be toward the end of the watch for
our counties. Most likely that would be after 300 AM. Hi-res
guidance suggests that it would be toward 500 AM in the far south,
spreading north. Otherwise, periods of showers with heavy rain will
continue to affect the region, especially over the western and
southern areas until we see a lull in the activity toward 200 AM to
300 AM. Then, the main event is expected to arrive later tonight in
the south, spreading north Friday morning. Additional tornado
watches are expected for central NC after 700 AM Friday.

Periods of showers/rain overnight, heaviest southwest. Breezy east
winds becoming windy late. Temperatures holding in the 70s.

Previous discussion as of 305 PM Thursday...

Overview: Hurricane Helene`s track has changed little, and is still
forecast to make landfall in the Big Bend region of Florida this
evening as a major hurricane. Helene should weaken to a tropical
storm by Friday morning as it approaches the Atlanta metro area,
then become nearly stationary over central Tennessee as it weakens.
Rainfall this afternoon is still primarily due to a boundary that
has been persistent over the Appalachian Mountains over the last two
days. The bulk of this afternoon and this evening`s rainfall will be
from the Triangle west, but it appears that by midnight, most of the
forecast area should actually be dry, with all of the rain to the
west and south of the area. Rainfall will then quickly ramp up late
tonight into Friday morning, which is when the heaviest rainfall
rates are expected in addition to the greatest severe weather threat
due to a band of moderate to heavy rainfall associated with Helene.
Despite limited instability considering the time of day, strong wind
shear will bring an increased risk for tornadoes late tonight, but
more likely Friday morning. The high-resolution model guidance
continues the trend of moving the primary band of rain out of the
region slightly more quickly, and it appears that the bulk of the
rain should move north into Virginia by early Friday afternoon. An
isolated shower or thunderstorm could persist through the afternoon
hours along the VA/NC border. Overnight lows should be near 70, with
daytime highs ranging from the upper 70s across the north to the mid
80s in the southeast. A separate hydrology section is below.

Wind impacts: As Helene undergoes its extratropical transition, wind
gusts should increase across much of central NC late tonight through
Friday. The strongest winds with Helene will be near the center of
the circulation itself, but there should also be a core of stronger
winds associated with the band of precip that moves through the area
Friday morning/afternoon. 12Z HREF 90th percentile shows wind gusts
in the 35-40mph range from early Friday morning into the afternoon
hours. Bumped up wind speeds and gusts closer to the NBM 90-95th
percentile and have issued a Wind Advisory for a good portion of
central NC from midnight tonight through 6pm Friday. While it will
certainly be breezy, the northern Coastal Plain should be far enough
away from the strongest winds to warrant a Wind Advisory based on
today`s guidance.

&&

.SHORT TERM /FRIDAY NIGHT/...
As of 305 PM Thursday...

After the weather of the last couple days, Friday night`s weather
will be quiet. An isolated shower or thunderstorm could persist
through the evening hours north of US-64, but the rest of the night
should be dry. Wind speeds will also start to come down, with values
below 5 mph in most locations by the end of the night. Lows will be
in the 60s.

&&.

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 325 AM Friday...

A chance of showers and a few storms will persist Sun into Tue,
mainly each afternoon/evening and primarly across the N. Dry weather
will follow for mid week.

The upper low which will have absorbed Helene is expected to drift
slowly ENE over the Ohio Valley Sun/Mon, moving from NW KY to N WV.
This will keep our area within SW flow aloft and in the warm sector
at the surface, between the surface low well to our WNW and high
pressure centered off the Southeast coast. A diffuse frontal zone
extending E of the KY low across VA combined with upslope-directed
low level flow suggest the better chances for sufficient focus and
lift will be across the N including the Triad/Triangle regions Sun
and Mon. A surface low will develop in W NC early Mon and move into
central NC Mon night, bringing a surface cold front with it. As this
low is expected to deepen a bit as it pushes east off the SE VA/NE
NC coast by late Tue, we should see a shift of better rain chances
into NE sections Tue. The upper low over N WV will finally start to
shear out and weaken into an open wave before shifting E and
offshore Tue night, propelled by a strong northern stream wave
pushing through S Canada and the N CONUS, reaching Quebec and the
Northeast states Wed and pushing off the Northeast coast Thu. This
will put our area into a drier NW flow Wed, prompting a trend to a
dry forecast, then a secondary cold front associated with the strong
northern stream wave will move through Wed night, drawing a cooler
air mass into NC by Thu. Models are in fairly good agreement on this
scenario, although the Canadian has a deeper low over N Ontario mid
week and as such is cooler in our area by Thu. Will have temps 3-8
degrees above normal Sun/Mon, 1-6 degres above normal Tue/Wed, then
within a degree or two of normal Thu, although if the Canadian is
correct, it could be even cooler Wed and esp Thu. -GIH

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 110 AM Friday...

Adverse aviation conditions are expected over much of central NC,
primarily all but the far NE, from early this mornig through this
afternoon. The worst conditions, which will be in the S and W
Piedmont, will include low cigs, periodic strong wind gusts, and a
few hours of low level wind shear. The center of what is now
Hurricane Helene is located over extreme S GA and will track quickly
north through GA through daybreak. While the current rainfall over
central NC is mostly light, cigs are largely IFR (with some MVFR far
NE), and these conditions should hold through this morning, with
gradual improvement to MVFR then VFR S to N through the day. This
lull in rain will last until around 10z, when a strong tropical
rainband will begin to lift NE through central NC, lasting through
about 20z. As this rainband passes through central NC terminals SW
to NE, at any given location, a few hours of torrential rains
producing MVFR-IFR vsbys are likely, along with enhanced wind gusts
and a potential for isolated tornadoes. In addition, a period of low
level wind shear is expected, primarily during 10z-16z this morning,
however strong surface gusts and very strong and shifting winds with
height will dominate through this entire TAF valid period at all
sites, dangerous aviation conditions for smaller aircraft in
particular. Once the intense tropical rainband lifts N and NE of the
area, after about 21z, VFR conditions are expected through the end
of the TAF valid period. Surface winds will be mainly from E and
ESE, shifting to be from the SE and SSE this morning, and finally
from the S this afternoon, gradually diminishing starting mid to
late afternoon.

Looking beyond 06z Sat, sub-VFR cigs may return esp across the NE
(RDU/RWI) after 08z early Sat morning, lasting until improving to
VFR by mid morning. Otherwise, VFR conditions will dominate through
Tue, with possible exceptions late Sun (rain chances mainly
INT/GSO), Mon afternoon (rain chances areawide), and early Tue
morning (chance of sub-VFR fog). -GIH

&&

.HYDROLOGY...
As of 305 PM Thursday...

Will issue a Flood Watch for the Piedmont and Sandhills region of
central NC for tonight through 6pm Friday.

Multiple rounds and bands of rain and thunderstorms will spread
north across central NC through Friday. Given recent wet
conditions, streamflows across Central North Carolina are
significantly above normal per 714 day USGS stream flows. NASA
SPoRT soil moisture percentiles are above the 90th percentile in the
010 cm and 040 cm layer across the southern coastal plain. In
addition, 1-3 hr hour Flash Flood Guidance is essentially below 2
inches across most of the Piedmont.

While the heaviest rain associated with Helene will be focused
across the foothills and mountains, a general 1-3 inches with
embedded heavier rain rate will cause a risk of flash flooding
through late Friday afternoon. This will be especially true where
creeks and streams are already swollen, and there are even some
areas with ongoing road closures owing to rainfall over the past 2
to 3 days. Lower rainfall totals and a reduced threat of locally
heavy rain across the northern and central Coastal Plain results in
a reduced flood threat and have omitted those locations from the
watch.

Main stem river flooding is not expected to be as significant of an
issue based on the 1-3 inch rain forecast, although heavy rates in
the vicinity of the Rocky River near Norwood, which drain from west
to east and may see heavier rain upstream, and also the routing of
significantly heavier rainfall in the upper reaches of the Yadkin
River may cause some flooding in the Yadkin basin. The Neuse and Tar
are also abnormally high with the Neuse at Smithfield currently in
minor flood.

&&

.CLIMATE...

Record High Minimum Temperatures:

September 26:
KGSO: 69/2005
KRDU: 73/1993
KFAY: 73/1930

September 27:
KGSO: 69/2011
KRDU: 73/2011
KFAY: 73/2017

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch through this afternoon for NCZ007-021>025-038>042-
073>077-083>086-088-089.
Wind Advisory until 6 PM EDT Friday for NCZ007-021>025-038>042-
073>077-083>086-088-089.

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Badgett
SHORT TERM...Green
LONG TERM...Hartfield
AVIATION...Hartfield
HYDROLOGY...Blaes
CLIMATE...RAH