FOUS30 KWBC 150743
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
343 AM EDT Mon Sep 15 2025

Day 1
Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL OVER PORTIONS OF
EASTERN NORTH CAROLINA AND SOUTHEASTERN VIRGINIA...

Current WV satellite indicates a maturing mid-level trough situated
just off the SC/GA coast with a surface low analyzed 150 miles 
east of KILM, meandering around as the upper pattern evolves. 
Expectation is the surface low to be pulled northwest over the 
course of the D1 with a closer proximity to the NC coast by later
this afternoon and evening with a strong east to northeast flow
anticipated over the northern flank of the SLP. Current NAEFS
ensemble output is forecasting a stout +2/+3 deviation u-vector
wind component with origins straight off the Atlantic, a signal
coincident with a robust low-level moisture advection regime into
the northern and western flank of the low pressure center. PWATs
are anticipated to climb closer to +1.5 deviations above climo,
good enough for outputs within the 1.5-2" mark across much of
eastern NC into the VA Tidewater. The persistence in the low-level
flow and modest ascent located within the maturing deformation axis
will lead to a long period of heavy rainfall situated across the
aforementioned areas above, allowing totals to reach between 2-4"
over areas along and east of I-95 and north of US70 in NC, and
between 1-3" across the VA Tidewater. 

00z HREF is pretty robust in the depiction for the above totals 
forecast with some embedded convective elements likely to spur 
rates between 1-2"/hr at times, mainly across northeast NC where 
strongest 850-700mb FGEN signals align early this evening into the 
overnight hours. HREF neighborhood and EAS probs for >2" are pretty
high for the region with the neighborhood >3" signal settling 
between 50-90% for the zone referenced above in NC. Antecedent 
drier soils leading in will help curb some of the flash flooding 
concerns initially, but the long-standing heavy rain threat, and 
embedded convective potential the second half of the forecast could
lead to isolated/scattered bouts of flash flooding as the event 
continues. The previous MRGL risk was expanded to align with the 
trends in the >3" neighborhood prob signal in the HREF, and to 
account for the latest ECMWF EFI signal extended a bit further west
than where we had the previous MRGL risk located. 

Kleebauer


Day 2
Valid 12Z Tue Sep 16 2025 - 12Z Wed Sep 17 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS
OF THE SOUTHWEST, THE CENTRAL HIGH PLAINS, AND VIRGINIA/NORTH CAROLINA...

...Southwest...

Scattered convective pattern will initiate on Tuesday afternoon and
early evening before fading with the loss of diurnal heating.
Current progs are for convection to be tied closer to the terrain
across southeast AZ into southern NM with isolated signatures of
>1"/hr plausible in the stronger cell cores. These areas generally
prone to runoff due to terrain complexities, as well as remnant
burn scars present in some locations. Maintained continuity from
inherited MRGL risk with some minor adjustments to remove El Paso proper.

...Central High Plains...

Strong shortwave trough ejection out of the interior Northwest will
lead to convective development and regional enhancement across the
Central High Plains. Greatest ascent is aligned with the diffluent
region of the mid-level shortwave with left-exit region dynamics
likely to maintain a prevalent heavy rain signature across the
western third of NE down into neighboring northeast CO and
northwest KS. Heaviest rain could remain just outside of the risk
area according to some guidance leading to low probability of flash
flooding due to the occurrence within the western Sand Hills.
There's still a good agreement on localized maxima within the hi-
res ensemble means, pin-pointing the area west of North Platte, NE
as one of the favorable spots for convective impacts. FFG's in this
corridor are lower than the neighboring Sand Hill domain, so the
MRGL risk remains relatively small. 

...Virginia and North Carolina...

Our surface low will mature and occlude by Tuesday afternoon as the
closed height fields indicate the 850/700/500 mb lows becoming
vertically stacked leading to a slow decay of the surface low by
the second half of the period. Persistent heavy rain potential will
linger across eastern NC up into the VA Tidewater leading to
multi-day totals reaching 2-4" with locally upwards of 6-7" over
the span of 48 hrs. Despite the drier soils leading into the event,
the cumulative effect will lead to areal flooding concerns for
portions of the above locations. Some westerly push of the heavier
QPF is progged in the front half of D2 leading to some areas in
north-central NC up through south-central VA possibly sneaking into
the flash flood threat. The only good news is the weakening surface
low will lead to degrading rates eventually, and slow wane on the
threat. The MRGL risk inherited was maintained with some minor
westerly expansions to account for recent trends in the ensemble means.

Kleebauer


Day 3
Valid 12Z Wed Sep 17 2025 - 12Z Thu Sep 18 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PARTS OF THE
NORTHERN AND CENTRAL PLAINS, SOUTHERN HIGH PLAINS, AND SOUTHEAST FLORIDA...

...Northern and Central Plains...

A strong mid-level shortwave trough will eject into the WY Front
Range and eventually close off across NE generating a maturing lee
cyclone across the Central High Plains. The setup will likely cause
quite a robust deformation signature on the northwest flank of the
cyclone with ensemble mean QPF placement situated over western NE
up through southwestern SD, arcing back into the nose of the warm-
conveyor belt on the northeast side of the system. This is a
classic mid-latitude lee cyclogenesis setup with a strong jet
coupling leading to broad large scale forcing and widespread precip
across the Plains. Eastern side of the cyclone will exhibit the
best convective potential while the deformation axis provides a
solid precip field with moderate to locally heavy rates for several
hrs. in that northwest side of the low. Totals >2" are forecast
within the means across western NE into SD with scattered elevated
QPF across the Missouri River basin located in eastern SD and NE.
This setup is conducive for at least some isolated to scattered
flash flood prospects considering the synoptic evolution. This was
enough to warrant a MRGL risk in those areas deemed the best chance
for heavy rain prospects. 

...Southern High Plains...

Maturing lee side low to the north will help drag a trailing cold
front through the Central and Southern High Plains on Wednesday.
The front will slip south and southwest once down near the
latitude of the OK Panhandle, leading to a more textbook backdoor
frontal progression as it enters into the northern TX Panhandle and
northeast NM. Flow begins to run more parallel to the boundary in
these zones when assessing forecast soundings from relevant global
deterministic. The key in the setup is a relatively solid
isentropic ascent pattern in a small zone bordering CO/OK/NM/TX
with cross-section views over the area displaying a classic sloped
low-level surface FGEN with strong omega correlating to rapid
ascent as the front progresses through the area. Locally enhanced
corridor of precip will transpire along and in wake of the front
with local maxima of 1.5" to as much as 3" plausible during the
event. This could be enough for an isolated flash flood threat,
especially in those smaller urban areas situated across the 4 state
intersection. A MRGL risk has been added to account for the threat. 

...Southeast Florida...

Stalled front with an enhanced moisture return across South FL will
lead to a heightened threat for flash flooding over the urban
centers of southeast FL. Deterministic output is scattered in the
exact location of the heaviest precip, ranging from the Keys up to
West Palm Beach and everywhere in-between. The setup is
historically favorable for flash flood concerns over the urban
zones of southeast FL with PWATs hovering between 2-2.3", a solid
1/1.5 deviations above normal. In coordination with the Miami WFO,
a MRGL was maintained for that urbanized coastal corridor between
West Palm down to Miami proper since this is the most likely
location for flash flooding in this type of setup. Will monitor
convective trends as we get closer to see if this necessitates any
expansion, or even a targeted upgrade.  

Kleebauer
$$
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