Flash Flood Warning 51, NWS Raleigh, NC

Area Forecast Discussion
National Weather Service Raleigh NC
400 PM EDT Fri Aug 30 2024

.SYNOPSIS...
Mid and upper-level high pressure will gradually weaken over the srn
Appalachians, while a quasi-stationary front will be modulated by
outflow and weaken over NC, through Saturday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 400 PM Friday...

A persistent mid-level anticyclone centered over the TN Valley and
srn Appalachians in 12Z upr air data will begin to weaken and
retreat sewd into srn GA through tonight, as a cyclone rapidly
deepens newd across Hudson Bay and a trailing synoptic trough and
height falls overspread the Great Lakes and mid MS Valley.  Weak,
generally nwly mid-level flow, and weak height falls (10-20 m) will
result across cntl NC. That light nwly flow regime may include a
slow-moving and small MCV or two from convection from swrn VA to
cntl NC this afternoon-evening.

At the surface, the backdoor segment of a synoptic front that
stretched ssewd across wrn PA, ern WV, and swrn VA was analyzed at
19Z near/across cntl NC from MWK/INT to near and modulated by
outflow at RDU, to RWI, to the nrn Pamlico Sound. The outflow-
modulated and reinforced front should drift swwd across the NC
Sandhills and wrn Piedmont through this evening.

Scattered pulse/multi-cell development should continue along the
outflow-modulated front as it moves into a strongly unstable and
uninhibited airmass ahead of it. VWP hodographs from KRAX and RAP
forecast soundings depict near zero to light nwly mean wind vectors,
which will favor nearly-stationary to very slow sewd individual cell
motions. When combined with observed PWs generally around 1.75", a
continued risk of isolated flash flooding will result, except some
scattered instances possible over urban (lower Flash Flood Guidance)
areas. Additionally, those high PWs and SPC objectively-analyzed
DCAPE of 1000-1200 J/kg will favor the development of wet
microbursts capable of isolated damaging gusts. While some weaker
convection may continue to bubble along outflow and/or the track of
lingering MCVs overnight, the marginal severe and/or flood risks
should wane after dark. Low temperatures tonight will be in the upr
60s to lwr 70s, with areas of stratus likely in the humid and rain
and nocturnally-cooled air.

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 320 PM Friday...

The upper level ridge that has been influencing the Mid-Atlantic
region the past few days begins to break down over the region
Saturday and shifts offshore by Sunday morning.  At the surface, a
lee trough is anticipated to develop over the western Piedmont
Saturday but could vary on location slightly as it will depend on
any interactions of left over boundaries from tonight's expected
convection. Saturday will start off dry in the morning but isolated
showers and storms are expected to develop mid/late morning with the
best chance of development in the NW Piedmont. By early afternoon
coverage will expand to scattered vs isolated and the best chance
for storms will will across the NW Piedmont and SE Coastal Plain.
However, a storm could develop anywhere over the CWA. Rain chances
reduce to 5-10% after sunset and diminish completely overnight.
Temperatures will be in the upper 80s in cooler spots to low 90s
elsewhere.  Lows overnight will be in the low 70s. Dewpoints in the
low to mid 70s will make it fell oppressive.

&&.

.LONG TERM /SUNDAY THROUGH FRIDAY/...
As of 322 PM Friday...

The immediate forecast challenge in the extended is the threat of
storms and heavy rainfall Sun and Mon with an approaching cold front
from the central and southern Appalachians. Model guidance remains
in good agreement that the best chance for showers and storms will
be in the late afternoon and through the evening hours. While deep
layer shear on Sun is marginal of 20-25 kts, MLCAPE suggested in
some of the models could approach 2000 J/kg. As such, SPC has
maintained a marginal risk of damaging winds. In addition to that
severe threat, WPC has retained a marginal risk of excessive
rainfall. This will be tied to slow storm motion, long skinny CAPE,
and mean layer flow of 15-20 kts. On Mon, while the effective front
will sag south of most of the area, the actual cold front will be
across northern sections and slowly move south through the afternoon
and evening. It still appears the highest rain chances will be over
the Sandhills to central Coastal Plain, where better forcing and
instability will reside.

Rain chances lessen Tue and Wed as a dome of high pressure over the
Mid-Atlantic states brings in more stable and cooler conditions. A
wedge-like scenario sets up with high pressure to our east-northeast
with northeasterly flow, at times gusty. Temperatures during this
period will be in the upper 70s to around the lower 80s, with lows
in the upper 50s to low 60s. As we transition to the latter part of
the week, guidance is still mixed on the potential for a southern
stream shortwave to possibly favor a developing surface low tracking
to our south. There still remain some ensemble members which take
the southern stream wave closer to our area and favor isentropic
ascent atop the lingering frontal zone for showers. Other solutions
keep the wave further south and more muted and suppressed. Given the
continued uncertainty, have left PoPs in the slight chance to low
chance range (20-30 percent). Highs should remain below normal for
the latter part of the week in the upper 70s to lower 80s.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
As of 210 PM Friday...

A quasi-stationary front stretching from near RWI to RDU to GSO will
provide a primary focus for slow-moving showers/storms for the next
couple of hours, with subsequent multi-cell development along rain-
cooled air (outflow) through this evening. Strong surface wind gusts
and brief flight restrictions will result beneath that convection,
while areas of IFR-MVFR stratus will develop in its wake late
tonight-Sat morning. Ceilings will lift through MVFR and/or scatter
to VFR through early Sat afternoon. Additional, widely scattered
showers/storms will be possible with afternoon heating Sat.

Outlook: Higher precip chances look warranted Sunday and Monday as a
slow moving front moves in from VA. Periods of non-VFR weather can
be expected at times through Monday. A post-frontal push of drier
air should work in from the north on Tuesday as high pressure
settles to our north on Tuesday.

&&

.CLIMATE...

Record High Minimum Temperatures:

August 30:
KGSO: 73/2005
KFAY: 75/1978

August 31:
KGSO: 73/2012

September 1:
KGSO: 74/2012
KRDU: 76/1932

&&

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

&&

SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...CA
LONG TERM...Kren
AVIATION...MWS/Leins
CLIMATE...RAH

Hazardous Weather Outlook
National Weather Service Raleigh NC
1053 AM EDT Fri Aug 30 2024

NCZ024>028-038>043-073>078-083>086-088-089-311500-
Orange-Durham-Franklin-Nash-Edgecombe-Davidson-Randolph-Chatham-Wake-
Johnston-Wilson-Stanly-Montgomery-Moore-Lee-Harnett-Wayne-Anson-
Richmond-Scotland-Hoke-Cumberland-Sampson-
1053 AM EDT Fri Aug 30 2024

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Unseasonably hot and humid conditions will result in heat index
values between 100 and 105 this afternoon.

In addition, scattered thunderstorms this afternoon through evening will
be capable of producing isolated instances of damaging wind gusts
and also heavy rain and risk of flooding of low-lying and urban
areas.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Showers and storms will be possible again Sunday and Monday. The
primary threat with these storms will be periods of heavy rain and
flooding, although isolated damaging wind gusts can't be ruled out.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

NCZ007>011-021>023-311500-
Person-Granville-Vance-Warren-Halifax-Forsyth-Guilford-Alamance-
1053 AM EDT Fri Aug 30 2024

This Hazardous Weather Outlook is for central North Carolina.

.DAY ONE...Today and tonight.

Scattered thunderstorms this afternoon through evening will be
capable of producing isolated instances of damaging wind gusts and
also heavy rain and risk of flooding of low-lying and urban areas.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Showers and storms will be possible again Sunday and Monday. The
primary threat with these storms will be periods of heavy rain and
flooding, although isolated damaging wind gusts can't be ruled out.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

Preliminary Local Storm Report
National Weather Service Raleigh NC
331 PM EDT Fri Aug 30 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0250 PM     Flash Flood      3 ENE Raleigh           35.84N 78.61W
08/30/2024                   Wake               NC   Broadcast Media

            Several cars stalled in flood waters needing
            water rescues.

&&

np

Preliminary Local Storm Report
National Weather Service Raleigh NC
346 PM EDT Fri Aug 30 2024

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0215 PM     Tstm Wnd Dmg     3 N Raleigh             35.87N 78.66W
08/30/2024                   Wake               NC   911 Call Center

            Numerous trees down across the northern half
            of the county.

&&

np

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