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206
FXUS62 KRAH 240736 RRA
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
335 AM EDT Tue 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 through mid-week.

&&

.NEAR TERM /TODAY AND TONIGHT/...
-- Changed Discussion --
As of 335 AM Monday...

...Multiple rounds of showers and storms...

...Isolated threat for Severe Storms and Flash Flooding across the
western Piedmont this afternoon/evening...


Very moist air will remain in place through tonight as a strongly
amplifying north stream trough digs south through the central Plains
today and into the middle MS Valley tonight. In response to this
digging upstream trough,  the upper ridge centered over the SE US
will move off the Atlantic coast. Meanwhile, at the surface, the
stalled front over SW portions of the Carolinas, though weakening,
will remain in place.

Multiple rounds of showers and storms are expected through tonight,
especially across the NW Piedmont. The first round of scattered
showers and storms is currently ongoing as weak disturbances eject
east across the area. Convective coverage is forecast to
expand/blossom in coverage, mainly across the northern Piedmont and
northern coastal plain, as the storms move east through late
morning/midday.

Round two is expected during the afternoon, with tempered daytime
heating/insolation within the moist 2-2.2" PWATS fueling moderate
buoyancy and the development of scattered showers and storms. The
greatest coverage is expected INVOF the weakening frontal zone
extending over the western Piedmont. Deep layer shear of 30-40 kts
will be sufficient to support a severe cluster or two, with damaging
winds and hail the primary threats.

Finally, the approach of the upper trough dynamics and continued
disturbances moving through the southern Appalachians will support
the re-development of showers and storms through the overnight
hours, with the bulk of the convection expected over the western
Piedmont. The multiple rounds of showers and storms will also bring
a threat of flash flooding this afternoon and into tonight. The
greatest flooding threat also appears to be across the western
Piedmont, where HREF PPM of exceeding 1"/3 hrs are maximized at 50-
70% and probability of exceeding 3"/6 hr are maximized at 40-50%.

Under extensive lows clouds, highs in the lower/mid 70s north to
lower/mid 80s south. Lows 65-70.
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&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
-- Changed Discussion --
As of 335 AM Tuesday...

An upper low at the base of the upper trough extending from the
Great Lakes to the Lower MS Valley will become cut-off Wednesday.
Central NC will lie sandwiched between this  wave trough and the
upper anticyclone off the SE US coast. We will actually see a brief
reprieve from the moist airmass as drier air off the SE coast
spreads west into the area. Meanwhile, the deeper plume of moisture
will get funneled up the spine of the Appalachians as eventual
Tropical Cyclone Helene gains strength as it moves north into the
GOM. At the surface, there are still signs of the stalled front
across southwest Piedmont.

After a late morning/mid day lull in precip/rain, isolated to
scattered storms will develop during the afternoon, with the best
coverage expected across the western Piedmont.

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.
-- End Changed Discussion --

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
As of 335 PM Monday...

Wednesday and Wednesday night: Aloft, a low will cutoff and meander
over the ARKLATEX region as the northern stream trough continues
eastward through the Great Lakes and Northeast. Meanwhile, high
pressure will ridge northwestward through the Carolinas/lower mid-
Atlantic. At the surface, high pressure over eastern Canada will
ridge sswwd along the Northeast and mid-Atlantic coasts. Meanwhile,
what is currently Potential Tropical Cyclone Nine will lift
northward into the eastern Gulf of Mexico, then is expected to
deepen and move quickly nwd through the eastern Gulf toward the Big
Bend area of FL. An inverted trough will extend nwd from the Gulf to
along the srn/ctl Appalachians, west of the aforementioned ridge, as
another trough extends ssewd through the OH Valley/nrn Appalachians
from a low moving ewd through the nrn Great Lakes. The confluent
sly/sely flow will advect warm, moist air into the area. There will
likely be plentiful cloud cover, which may limit daytime heating and
thus potential instability. The 12Z NAM forecast soundings show
MUCAPE around 1000 J/Kg, effective shear around 30 kts and PWATs in
the 1.5-1.8 inch range across central NC during the aft/eve. Given
the warm, moist, potentially unstable environment, expect any
ongoing showers to continue into the day Wed and cannot rule out
some storms as well. Highs should range from around 80 degrees NW to
mid 80s south with lows mainly in the mid 60s to around 70 degrees.

Thursday and Friday: A Rex Block will set up over the eastern US,
with the low over the ARKLATEX and the low over southeast Canada,
bisected/blocked by a ridge extending nwwd from a high off the
Southeast US coast and another high over the Desert Southwest
ridging newd into the Great Lakes. The other feature at play is
Potential Tropical Cyclone Nine, which is forecast to move inland
near the Big Bend area of FL on Thu, lift nwd through the Southeast
US Thu night, then get wrapped up into the low over the ARKLATEX
Fri. It is yet to be determined if the Block will be strong enough
to keep PTC9 with the low or whether it will shear out over the nrn
mid-Atlantic Fri night. There is still some uncertainty with the
expected track of PTC9 as it moves nwd through the Southeast US and
where it goes thereafter. Latest operational model guidance suggests
the center may stay west of central NC (NC mtns), putting central NC
in the NE quadrant of the system on Fri. Heavy rainfall/flooding,
strong, gusty winds, and tornadoes will all be possible from Thu
night through Fri night. Latest rainfall forecast from the WPC has 2-
2.5 inches along the Yadkin River to half an inch/inch in the east.
With the overcast, rainy conditions Thu and Fri, highs should be
near to slightly above normal, mid/upper 70s to low/mid 80s, while
lows will be well above normal, in the mid/upper 60s to low 70s.

Saturday onward: The mid/upper level pattern may become more of an
Omega block than a Rex block over the weekend as the low to the
northeast shifts sewd over the nrn Atlantic, pushing the high/sub-
tropical ridge wwd, while the other low sits over the ARKLATEX
region. At the surface, as the remnants of PTC9 tries to continue
nwd along the Appalachians Fri night/Sat, high pressure over
southeast Canada will shift swwd through the Northeast and mid-
Atlantic coasts and overtake the system by Sat night/Sun. The medium-
range guidance diverges quite a bit over the weekend and it is
unclear whether high pressure will dominate or whether a low will
lift through and along the Southeast US coast late Sun/Mon. If, when
and how much precipitation there will be will depend on how that all
plays out, so will hold off on those specifics for now. As for
temperatures, generally expect temperatures to gradually decrease
from Sat to Mon.

&&

.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 145 AM Tuesday...

LIFR to MVFR flight conditions, lowest at KINT and KGSO, will
continue through late morning, with some slight, 1-2 category
improvement( during the afternoon. Ceilings will lower back down
this evening and tonight, ranging from LIFR in the west to IFR/MVFR
in the east.

Multiple rounds of showers and storms are expected through the
forecast period, especially at KINT and KGSO. The first round
of scattered showers and storms is expected to move east across the
area through mid morning, with northern TAF sites having the best
chance of seeing rain/reduced VSBYS. Round two is expected during
the afternoon, as tempered daytime heating/insolation fuels moderate
buoyancy/instability and the development of scattered showers and
storms. Finally, the next of disturbances spreading into the area
from the west will bring a third round of showers and storms  during
the evening and overnight hours, with the bulk of this convection
expected at KINT and KGSO.

Outlook: A persistently, unseasonably moist air mass in place over
cntl NC will favor repeated overnight-early day low ceilings and
visibility restrictions and also an above average chance of showers
and storms this week. The chance of both may be exacerbated by the
influence of Potential Tropical Cyclone Nine late Thu through
Friday.


&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...CBL
SHORT TERM...CBL
LONG TERM...KC
AVIATION...CBL/MWS