574
FXUS62 KRAH 231844
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
245 PM EDT Mon Sep 23 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 /THROUGH TONIGHT/...
As of 1130 AM Monday...

While minimal forecast changes were needed with the gridded morning
forecast update, recent HRRR guidance depicts an increasing signal
for training convection and a risk for heavy rain/flooding late
tonight and particularly Tue-Tue night, along the surface front
forecast to waver over the Piedmont of the Carolinas for the next
couple of days.

Additionally, NHC has initiated advisories on Potential Tropical
Cyclone Nine, which may at least indirectly impact cntl NC as it
tracks through the vicinity of the srn Appalachians later this week.

.PREV DISCUSSION... /ISSUED 345 AM EDT Mon Sep 23 2024/

...Increasing rain chances from the west this evening and tonight...

Aloft: Weak H5 rises are expected over the region as the upper ridge
over the GOM builds towards the Florida Peninsula and across the SE
US. Weak impulses ejecting NE out ahead of the positive-tilt trough
advancing east over the MS Valley, will move through the southern
and middle Appalachians and into the southern mid-Atlantic region
tonight.

At the surface: Yesterday`s back-door cool front appears to be in
the process of stalling out across upstate SC. A northward wavering
of the front into southern/southwestern NC is possible later this
afternoon and evening as a ridge of weak surface high extends down
the Atlantic coast.

In response to the feed of low-level dry air along the coast, the
extensive low overcast is expected to erode along it`s eastern edge
later this morning and into the afternoon, while likely persisting,
in some diminished fashion, across the NC Piedmont through much of
the day. Exactly where and when the breaks/partial breaks in cloud
cover develop will be a decisive factor in today`s forecast highs.
Thus, a little more challenging than most days. Highs ranging form
mid 70s north to mid 80s.

As far as rain chances, while an isolated shower/storm is possible
INVOF the surface front, it looks mostly dry through the afternoon.
Then during the evening and overnight hours, rain chances will
increase from west to east as strengthening WAA, fueled by the
aforementioned upper level impulse with a similar signal for ins,
support scattered showers and storms. Rainfall amounts of 0.10 to
0.25" is expected across the NC Piedmont, with some localized higher
amounts near 0.50" possible.

Lows again in the lower 60s NE to upper 60s south.

&&

.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 245 PM Monday...

The stalled boundary is forecast to be draped NW to SE from the
southern/western Piedmont, arcing into the southern Sandhills to
start the period. With time, the boundary will lift north as a warm
front during the afternoon and evening, perhaps reaching southern VA
come Wed morning. Aloft, shortwave troughing will be present across
the Mid-Mississippi Valley, while ridging will be over the southwest
Atlantic. The resultant flow will be southwesterly, with a few
disturbances tracking through in the morning, aftn/eve, and
overnight period.

Morning isolated to scattered showers or storms will be possible
across eastern sections of central NC as a disturbance tracks across
the area. The highest PoPs are favored over the Triangle,
east/northeast Piedmont, and into the Coastal Plain. Outside of
these showers, widespread low stratus and patchy fog will be present
north of the aforementioned boundary. As the front starts to lift
north, however, we should see erosion of the stratus from SW to NE,
slowest in the north and northwest. As a result, highs should range
below normal in the mid 70s in the far north, to above normal in the
mid 80s in the S and SW.

Another round of scattered showers and storms will develop in the
late afternoon/evening, continuing into the overnight hours as a
secondary disturbance tracks through. The front and differential
heating will aid forcing for ascent, along with 2000-2500 J/kg of
MLCAPE. A Marginal Risk of severe storms is still in place across
the western Piedmont, owing to deep-layer shear of 35-40 kts and
DCAPE of 800-1000 J/kg, supportive of a damaging wind threat.
Isolated large hail cannot be ruled out as well, given nearly
uniform hodographs in place. CAMs vary on where storms initiate, but
a general consensus appears across the far western Piedmont, before
advancing east-northeast in the evening to overnight. Highest PoPs
are across the NW and Triad and lowest in the SE.

As we go into the late-evening hours, storms appear to become at
least partially elevated, and PW`s upwards of 2 inches (140-percent
of normal) with SW WAA aloft will support a flash flood threat in
training storms atop the lingering boundary. The 12z HREF is showing
a signal for 2-3+ inch rainfall totals in two areas. One area
stretches along and just SW of the Triad into VA, while a second
area stretches along US-1 into the Triangle. Given these two
regions, WPC has introduced a Marginal Risk for excessive rainfall
over much of central NC to cover the uncertainty. Convective
coverage should start to favor northern areas overnight into Wed
morning as the boundary slowly shifts north. Overnight lows will be
in the mid to upper 60s.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 335 AM Monday...

Increased chance of precipitation through the long term period
despite the uncertainty with respect to the development and track of
the tropical cyclone in the Gulf of Mexico mid week.

On Wednesday, a cold front moving east across the OH and TN valley
will weaken as it moves into the region Wednesday afternoon. Expect
scattered showers and isolated storms in the afternoon especially in
the NW Piedmont as models are depicting afternoon CAPE values range
from 500-1000 J/kg. With that, high temperatures in the NW will
range from the upper 70s to low 80s and in the SE low to mid 80s.

For the rest of the week and into the weekend, deterministic models
are showing a tropical cyclone landfall somewhere along the Florida
Panhandle or Big Bend area of Florida Thursday afternoon or evening.
While the intensity, timing, and location is uncertain for now,
models have come in more agreement in the past few model runs.
Either way, Central NC is expected to begin to see some impacts as
early as late Thursday night/early Friday morning. While most models
show the center of the storm staying west of the region, increased
moisture from the Atlantic will help  support showers and storms
through the day Friday. For the weekend, the forecast will depend
largely on the the timing and location of the TC remnants, thus kept
low end slight chance PoPs for Saturday and Sunday but with very low
confidence.

Temperatures will be a few degrees above normal on Thursday with
highs in the upper 70s to low 80s. The rest of the week/weekend
becoming near average for the the rest of the week and weekend with
highs ranging mid/upper 70s to low 80s.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
As of 250 PM Monday...

IFR-MVFR ceilings centered over the NC Piedmont will continue to
lift with diurnal heating through this afternoon, with some
potential for brief scattering to VFR by this evening. Any
scattering over the Piedmont should be short-lived, however, as low,
IFR-MVFR ceilings are likely to redevelop in a persistently humid
regime in place overnight-Tue morning. The low overcast should then
slowly lift with diurnal heating once again during the late morning
through afternoon Tue. Additionally, there will be a chance of
showers and perhaps a few storms tonight and especially with diurnal
heating on Tue, as a series of disturbances aloft overspread and
interact with a frontal zone that will waver over the Carolinas.

Outlook: A persistently, unseasonably humid airmass 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 Fri-Sat.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS/CBL
SHORT TERM...Kren
LONG TERM...CA
AVIATION...MWS