000
FXUS62 KRAH 210225
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1025 PM EDT Sat Jul 20 2024

.SYNOPSIS...
A series of convectively-amplified disturbances in moist,
southwesterly flow aloft will overspread and interact with a surface
front that will weaken over the Southeast and southern Middle
Atlantic through early this week.

&&

.NEAR TERM /TONIGHT/...
As of 1025 PM Saturday...

00Z upr air data depict a belt of convectively-perturbed and
modestly strong, 15-30 kts of wswly 700-500 mb flow over the
Southeast, between a strong subtropical ridge over the swrn N.
Atlantic and a positive tilt trough from ern Canada swwd through the
Great Lakes and srn Plains. Within that flow, a couple of MCVs over
n-cntl SC and the srn Piedmont of NC, over Fairfield Co. and
Cabarrus Co., respectively, will track generally enewd across cntl
NC tonight.

At the surface, a composite outflow/effective surface front was
evident in 02Z radar and surface observational data from an
occasionally SVR-warned storm cluster near KOCW, swwd to KCTZ, then
wwd to EQY. As that convectively-reinforced boundary settles slowly
sewd across the srn NC Piedmont, Sandhills, and srn Coastal Plain,
it will collide/interact with the sea breeze and other outflow from
more-isolated cells from sern NC and nern SC, within an environment
characterized by lingering weak MLCAPE of generally 500-1000 J/kg.

The track of the MCVs generally atop and parallel to the composite
outflow/effective front will favor additional, scattered to numerous
showers/storms, with a lingering risk of heavy rain and isolated
flash flooding, tonight. Meanwhile, the environment north of the
front has been more-uniformly rain-cooled and stabilized into the
lwr 70s across the Piedmont and nrn/cntl Coastal Plain and where the
threat of showers/storms has consequently diminished.

Areas of very low overcast will otherwise continue to develop and
expand within the heart of the rain-cooled air across the Piedmont
and nrn Coastal Plain, with temperatures mostly in the lwr-mid 70s.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
As of 242 PM Saturday...

A Marginal (level 1 of 4) risk of excessive rainfall continues
Sunday and Monday.

On Sunday, a trough will be roughly located over the Mid-Mississippi
Valley, with ridging over the southwest Atlantic. At the surface,
weak low pressure will be situated along the western TN valley. The
stationary front from today will still be present across southern
VA, although some remnant outflow boundaries from Sat will likely be
present across the region. With the front to our north, the main
forcing would appear to be from what models are showing to be
another impulse at mid-levels. This energy looks to come out of
eastern GA and SC during the late afternoon and evening hours.
Additional forcing could come from the sea-breeze interacting via
outflow boundaries. The 12z CAMs are mixed on coverage and location,
but the global models and ensembles are favoring the highest storm
chances across the southern Piedmont to southern Coastal Plain, and
expanding northward as the energy tracks through. Have kept high PoP
chances as a result, centered on the aftn/eve. Flash flooding will
again be possible with 15-20 kts of mean-layer flow and continued
anomalous PWs. Highs look to be a tad warmer than Sat in the upper
80s to around 90. A second wave of energy could favor overnight
convection into Monday so have kept chance PoPs during the latter
half of Sun night. Overnight lows to be in the upper 60s/low 70s.

On Monday, the trough from Sun will move from the OH valley into the
lower Great Lakes. Broad low pressure at the surface should be
located over the lower OH valley. The stationary front should inch a
tad further north into northern VA. With the front currently
anticipated to be well removed from central NC, forcing for
convection at the surface may be more subtle than Sun. A surface
trough appears to be in place across the southern Appalachians and
western NC. At mid-levels, guidance shows yet another impulse coming
out of the SW flow from western SC. This impulse appears as a
possible driver for afternoon and evening showers and storms once
again. A jet streak near the region could also aid divergence aloft.
Storms may additionally fire along the trough in the NC Foothills,
tracking east into the evening hours. Deep layer shear is somewhat
higher than prior days of ~30 kt, with similar or higher
instability. While we are not outlooked, a few stronger storms could
produce damaging wind gusts. On top of that, heavy rainfall
remains a threat. Convective initiation may be slower to develop
with the front removed from the area. Thus, highs may be a tad
warmer in the mid 80s N to low 90s central/south.

&&

.LONG TERM /TUESDAY THROUGH SATURDAY...
As of 300 PM Saturday...

...Above normal rain chances will lead to seasonable to slightly
below normal temperatures next week...

...Widespread beneficial rainfall is expected to bring additional
drought improvement...

Sandwiched between persistent upper level troughing that stretches
south from the Great Lakes to the southern US Plains and a strong
subtropical ridge that extends over the western Atlantic and SE US,
deep SW flow will keep a plume of deep moisture, featuring PWATS of
2.3-2.5" (120-140% percent of normal), entrenched across the region
all next week. DPVA via shortwave impulses embedded in the SW flow,
in tandem with daytime heating and interaction with
seabreeze/outflow will lead to high/likely chances of showers and
storms each day. The super ensemble mean average cumulative rainfall
during the long term period is between 1-3", with higher amounts
possible within any heavier convection. The expected rainfall
amounts should lead to additional improvement in drought conditions
across NC.

Timing discrepancies still need to be resolved, but a frontal
passage sometime next weekend could mark an end to the convectively
wet pattern.

The above normal rain chances and associated increase cloud cover
and will keep the heat at bay, resulting in seasonable to slightly
below-normal high temperatures. Highs generally 85-90. Lows in the
lower to mid 70s.

&&

.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
As of 815 PM Saturday...

Showers and storms will continue along ahead of a composite outflow
boundary/effective cold front, evident in 00Z radar and surface
observational data from near ETC to TTA to JQF, that will continue
to settle sewd across RWI and FAY this evening. Trailing, light
stratiform rain and mainly MVFR visibility restriction will linger
for 2-3 hours behind the passing front and convection. In the most
extensive rain-cooled air behind the front, LIFR-IFR ceilings are
likely to develop over the Piedmont and perhaps RWI overnight, while
shorter-lived, IFR-MVFR ones will be more likely at FAY. All
ceilings should lift and scatter to VFR between 14-18Z Sun, followed
by a redevelopment of scattered afternoon-evening showers and
storms.

Outlook: There will be a high chance for showers and storms each day
through Thu, as we stay in a moist and unsettled pattern. The chance
for late-night-through-mid-morning sub-VFR clouds and briefly sub-
VFR vsbys will also continue through mid week. -GIH

&&

.CLIMATE...

Record High Minimum Temperatures:

July 20:
KGSO: 75/2019
KRDU: 76/2020

July 22:
KGSO: 77/2011
KRDU: 78/2011

July 23:
KRDU: 78/2011
KFAY: 79/2017

July 24:
KRDU: 79/2011
KFAY: 79/1945

July 25:
KFAY: 78/2016

July 26:
KGSO: 76/2016
KRDU: 77/2010

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...MWS
SHORT TERM...Kren
LONG TERM...CBL
AVIATION...MWS/Hartfield
CLIMATE...RAH