574
FOUS30 KWBC 160055
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
855 PM EDT Sun Jun 15 2025

Day 1
Valid 01Z Mon Jun 16 2025 - 12Z Mon Jun 16 2025

...A MODERATE RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF
SOUTHEAST VIRGINIA AND NORTHEAST NORTH CAROLINA...

...Mid-Atlantic and Central Appalachians...
The main flash flood risk this evening will be across portions of
southeast VA into eastern NC. Recent HRRR runs indicate the
highest rainfall magnitudes will be over eastern NC...and
observational trends support that idea as well. Some additional
rainfall totals over 3" appear likely, resulting in an isolated to
scattered flash flood threat. A MDT risk was maintained across
portions of southeast VA into northeast NC where a locally
significant flash flood risk continues this evening. The highest
additional rainfall magnitudes may very well end up near or just
south of the MDT risk area over eastern NC...however higher FFG
over this area precludes the need for an expansion of the MDT
risk...although do consider these areas to be within a higher end
Slight risk.

Elsewhere within the broad Slight risk covering much of WV and VA
the flash flood risk is waning...however a localized threat likely
continues given the saturated conditions and periodic areas of low
topped convection developing near the slow moving low and mid
level shortwave energy.

...Arkansas into Missouri...
An uptick in the flash flood threat is likely this evening across
central AR into southeast MO. Plenty of instability remains, and
an uptick in the low level moisture transport this evening is
resulting in more robust convective development. Not enough shear
to really organize activity, and also not much of an upstream
instability pool to work with. Thus would expect convection to
erode instability fairly quickly as it tries to grow upscale. This
would suggest an initial uptick in the flash flood risk this
evening...with a gradual waning of activity as the night
progresses. This should keep the threat at Slight risk
levels...although with PWs over 2" rainfall rates will be high,
and thus locally significant flash flood impacts can not be ruled
out.

...Northern Plains...
Slow moving convection near a remnant MCV will keep a localized
flash flood risk ongoing over IA this evening. The more organized
convection is expected over MT where the ongoing supercells are
expected to grow upscale into an MCS and track eastward across MT
and eventually into the Dakotas. The quick forward motion should
limit the coverage and magnitude of the flash flood risk, although
do note moderate to high probabilities of exceeding 1" in an hour
as this activity tracks eastward (~60% in the HREF and 90% in the
REFS). Even seeing a 20-40% chance in these high res ensembles of
exceeding 2" in an hour rainfall. Thus despite the quick forward
motion some FFG exceedance is likely tonight as the activity moves
eastward. How this FFG exceedance translates to impacts is a bit
less certain...and generally think flash flooding will remain
isolated in nature. Thus we will just stick with a Marginal
risk...but some localized significant impacts can not be ruled out
if/where rainfall is able to exceed 2" in an hour.

Chenard


Day 2
Valid 12Z Mon Jun 16 2025 - 12Z Tue Jun 17 2025

...A SLIGHT RISK OF EXCESSIVE RAINFALL EXISTS FOR PORTIONS OF THE
MID-ATLANTIC, CENTRAL APPALACHIANS, AND OHIO VALLEY...

...Mid-Atlantic to Central Appalachians...

20Z Update: Convective focus along a stalled quasi-stationary
front will lead to another period of locally heavy rainfall with
training potential existing over portions of North Carolina. The
setup is just a continuation of a broad convective regime with a
general alignment of stronger convection within the confines of a
front that will lie from Western PA down through Northern and
Eastern WV, Southwest VA, arcing back towards Eastern NC.
Relatively buoyant environment and elevated PWATs running +1.5 to
+2 deviations will be sufficient in producing local rainfall rates
between 1-2"/hr across much of the above zones with the Eastern NC
area more likely to see closer to 2-3"/hr in heavier cores as
projected within the latest hourly rate probs via the 12z HREF.
HREF blended mean QPF output is a general 0.5-1" in areal average
across Southwest PA down through Northern and Eastern WV, but
scattered deterministic signals of 2-3" are pretty common within
the latest suite. A more robust 1.5-2" areal average is positioned
from the NC Triangle across through Eastern NC with a general
maxima between RAH to Hatteras. The eastern fringes of the heavier
precip will be positioned over sandier soils leading to a naturally
lower probability for flash flooding compared to inland areas of
NC. Points north are a combination of low FFG`s and complex terrain
that will likely cause some problems with almost any heavier QPF
core that materializes. Given the signatures above, and a forecast
SLGT from the recent First Guess Fields in the interior Mid
Atlantic, a SLGT risk upgrade was generated for the D2 forecast
with a footprint extending from just east of RAH along I-40 and
points northwest up through Southwest VA, Northern and Eastern WV,
and Western PA.

Kleebauer

...Ohio Valley...

20Z Update: A persistent MCV will create an environment favorable
for locally heavy rainfall across portions of the Mid-Mississippi
Valley into the Ohio Valley. Area convergence under the general
circulation from the remnant complex will create a zone of enhanced
precip potential with most of the CAMs indicating the area from
far Western KY through the Ohio River Basin encompassing
IL/IN/KY/OH with the magnitude of heavier totals between 2-4". 12z
HREF neighborhood probs for >3" is pretty high (40-70%) along that
corridor of the Ohio River with the maximum depiction between that
intersection of IL/IN/KY. This is the general location of the
circulation when you assess the 500mb vorticity panels, so it makes
sense synoptically that the threat would converge over the
strongest mid-level ascent focus. FFG`s are relatively modest
overall, but with 1-2"/hr rate potential in any cell development,
this would be sufficient to exceed the hourly FFG`s currently, but
the biggest signal comes from the 3hr FFG exceedance probability
with the latest ensemble output showing 30-50% chances for several
3hr increments between 12-00z tomorrow. A targeted upgrade to a
SLGT risk is now in place over the aforementioned region for the
threat of flash flooding under the guide of a remnant MCV/low-
amplitude shortwave moving from the Mid-Mississippi Valley into
the Western Ohio Valley.

Kleebauer

...Dakotas to the western Great Lakes...

20Z Update: Little to no adjustment was necessary for the broad
MRGL risk as the previous forecast remains steadfast in its
presentation for locally heavy rainfall across the Upper Midwest
into parts of the Northern Plains. The heaviest rain is still
forecast to occur in the heart of the Sandhills of NE, an area that
will likely be void of many flash flood concerns due to the soil
composition and very high FFG`s in place.

Kleebauer

..Previous Discussion..

Consensus for locally heavy rainfall across portions of the
Northern tier of the CONUS remains favorable across a broad area
extending through the Dakotas, Nebraska, and the Upper Midwest on
Monday. It remains the case that some of the heavier rainfall is
expected over the Sandhills of Nebraska where flash flood guidance
is high, and therefore not rising to the level needed for a Marginal
Risk in that area. Elsewhere, there remains a scattered heavy rain
threat over the northern portions of the Upper Midwest at this
time, and therefore a Marginal Risk remains valid there.

Hamrick


Day 3
Valid 12Z Tue Jun 17 2025 - 12Z Wed Jun 18 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE MIDWEST, EASTERN OHIO VALLEY, AND CENTRAL APPALACHIANS

...Midwest...

20Z Update: The previous forecast SLGT was general maintained with
some expansion of the risk area to the southwest given the latest
trends slowly shifting the threat more into Northwestern MO and
far Northeast KS. The latest ML output is also leaning towards the
southern end of the envelope when it comes to the heaviest QPF
distribution, so it`s plausible the shifts will continue to trend
more into the I-70 corridor across KS/MO if this holds. For now,
wherever the threat materializes, there will be heavy rain with
totals likely between 3-5" in the hardest hit areas. Some training
potential is plausible considering the upwind trajectory behind the
vacating surface low as it cuts to the northeast. Will be
monitoring closely for both the positioning of the risk, and a
potential for a targeted upgrade if the magnitude of the precip
forecast increases, or focuses over some of the larger urban
corridors where flash flood potential is most likely. A higher end
SLGT is certainly forecast at this juncture.

Kleebauer

..Previous Discussion..

A well organized mid-upper level shortwave trough will eject
eastward from the Rockies to the central Plains Tuesday afternoon
into the early hours of Wednesday morning, and this will sustain
the development of a surface low that will develop along a frontal
boundary. Upper level dynamics will be favorable as the region will
be place under the right entrance region of the main upper level
jet, and incoming mid-level positive vorticity advection will
further aid ascent. Precipitable water values in the warm sector of
this surface low are expected to rise into the 1.75 to 2 inch
range and an increasing southwesterly low level jet that will
advect copious moisture into the system.

Model guidance has trended a little to the south over the past few
model cycles, with the greatest consensus for the heaviest QPF
across the southern half of Iowa and over the northern third of
Missouri, and extending to northeast Kansas and west- central
Illinois. Most model solutions have a broad corridor of 1-2 inches
with embedded 3-4 inch maxima within this region, with the majority
of this happening within the 18Z Tuesday to 6Z Wednesday time
period. The heavy rain that fell across portions of the Upper
Midwest is generally north of where this expected rainfall will be,
so grounds will not be saturated in most cases leading up to this
event. The inherited Slight Risk from the previous Day 4 outlook
will be maintained with a southward expansion to it, and a broader
Marginal Risk extending across South Dakota and eastward to include
the greater Chicago metro area.

Hamrick


...Ohio Valley and Central Appalachians...

20Z Update: The threat for a broader impact flash flood threat is
increasing as we move into Tuesday afternoon and evening before we
finally end the incessant heavy rain pattern generated by scattered
to widespread convection across parts of the Eastern Ohio Valley
into Western PA and the adjacent Appalachians. The upper pattern
will be a significant driver in the area precip coverage as we move
into Tuesday with large scale forcing on the rise as we see an
approach of a potent shortwave trough out of the Ohio Valley. Area
moisture field will be running ~2 deviations above normal with
forecast PWATs between 1.7-2" likely across much of Ohio, Eastern
KY, WV, and the western half of PA. The combination of a stagnant
elevated moisture regime and plentiful forcing will generate a
period of scattered to widespread thunderstorm activity migrating
across the above areas creating a heightened threat of flash
flooding when you take into consideration the compromised soils
from all the rainfall leading into the setup. The area of Northern
WV, Western PA, and Eastern Ohio is by far the most sensitive in
this pattern and the threat for heavy precip is as genuine as you
can get, in a synoptic sense. Ensemble depictions of 1-1.5" areal
average at a D3 lead is a testament to the threat and has a lot of
support from the QPF distribution within the latest ML consensus.
For now, a SLGT risk was introduced to encompass that corridor
referenced above in the Ohio Valley up through Western PA. If this
trend becomes more favorable in the QPF maxima exceeding 3" across
some of those more compromised areas, a further targeted upgrade is
plausible. This is a setup to monitor closely over the coming days.

Kleebauer


Day 1 threat area: https://www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: https://www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: https://www.wpc.ncep.noaa.gov/qpf/99epoints.txt