FOUS30 KWBC 281549
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1149 AM EDT Mon Apr 28 2025

Day 1
Valid 16Z Mon Apr 28 2025 - 12Z Tue Apr 29 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE RED RIVER VALLEY AND CENTRAL/SOUTHERN OKLAHOMA...

16z update...for Southern Plains...

A few 12z CAMs suggest a strong cluster/few super-cells that will 
be capable of intense heavy rainfall this afternoon across portions
of KS/OK into Northwest Texas. Recent heavy rainfall in the 
region, highlighted by NASA SPoRT 0-40cm saturation ratios over 
70-80% and well above normal in the 90-95% percentiles suggest 
little infiltration is expected even in rural locations. There 
remains sufficient uncertainty to the precise latitude of these 
individual cells or small clusters to have high confidence. 12z 
HREF probability have increased across the most saturated areas 
with greatest 1" and 2" per hour and 3-hour periods and now as high
as 30% across the most saturated areas of Southern Oklahoma. In 
coordination with local forecast offices, this is sufficient 
highlight a small upgrade to a Slight Risk mainly along the the Red
River into central OK where both meteorology and hydrology overlap
the most. 

Gallina

~~~~Prior Discussions~~~~

...Northern Plains & Upper Midwest...

The period in question will remain active on the rainfall front, but
a few key pieces will be missing, relegating flash flood prospects
closer to the MRGL risk category as inherited from the previous
update. Upper level progression from the Inter-Mountain West through
the Northern Plains and Upper Midwest will exhibit a decaying mid to
upper level structure of a closed ULL out west with a more sheared,
progressive pieces ejecting into the High Plains and propagating
northeastward through MN and northern WI. The evolution is such that
a reasonable upper forcing pattern will materialize with scattered
to widespread convective initiation located downstream of a broad
diffluent axis situated from the Front Range through the Upper
Midwest. Instability on the order of 1500-2500 J/kg of MUCAPE will
be present ahead of the mean trough with ample mid-level
perturbations ejecting into the northern tier of the CONUS during
the morning and afternoon periods. To round off the setup, a budding
140-150kt jet streak will be oriented over south-central Canada
providing a solid RER dynamic suitable for maintaining a more
organized precipitation element over the northern tier of the CONUS.
Despite the above support for convective prospects, the pattern will
be in the process of breaking down as the upper low out west becomes
a more open wave with the primary bulk of mid-level energy quickly
ejecting northeast with a textbook strong PVA to NVA signature as
the energy vacates over the northern Lakes. This setup has shifted
to a very front loaded convective scheme over the Northern Plains
into the Upper Midwest with a majority of the convective pattern
quickly ushering east-northeastward through the course of the
morning and afternoon periods. By the evening, remnant convective
elements will become more scattered in nature, eventually moving out
of the primary area of interest after nightfall leading to a
diminished threat for the end of the forecast cycle.

00z HREF EAS probs remain pretty elevated (50-80%) for at least 1"
across the eastern half of ND through Northern MN, but a sharp
decline in probs for >2" leading the case for more isolated to
widely scattered flash flood prospects in the given pattern. There
are some respectable probabilities in the neighborhood scheme for
>2" within the Arrowhead of MN back over the the Dakotas (50-80%),
but again a sharp decline once into the >3" fields limiting the
upper bounds of the potential. A few areas may see between 3-5" at
the peak, but those will likely be few and far between for an area
that is actually in a low-end drought overall. Considering the soil
type and antecedent dry conditions in the region, the inherited MRGL
was maintained with little change in the risk area over the Northern
Plains into the Upper Midwest.


...Central and Southern Plains...

The Central and Southern Plains will reside within a broad warm-
sector environment positioned between a vacated warm front pressing
north through the Mississippi Valley and a slow-moving cold front
through the High Plains with a secondary cold forecast to plunge
southeast through the Northern and Central High Plains by the end of
the forecast cycle. A fairly meridional upper pattern will end up
being a key factor in the eventual ejection of stronger shortwaves
out of Chihuahua, MX, barreling northeastward through the Southern
Plains with scattered to widespread thunderstorm development along
and east of a dry line situated over West TX. The combination of
relevant buoyancy/instability positioned over the Southern and
Central U.S. coupled with favored regional ascent and
thermodynamics will create a period of late-afternoon and evening
convective development capable of localized flash flood prospects.
Recent heavy rain episodes have contributed to an elevated soil
moisture presence from the Red River Basin up through much of OK
into southeast KS, and MO. Rainfall totals up to 2-3" in a short
time frame will be capable of causing flash flooding within the
bounds of those areas that exhibit those moist top-layer soils
since the time frame for recovery will have been short. 00z HREF
neighborhood probs for >1" are respectable (50-70%) within portions
of the Central and Southern Plains with the focus generally over
north-central OK, Concho Valley, and Western Rolling Plains of West
TX. Probabilities for >2" are very low leaving the threat for
flash flooding fairly conditional and likely more reserved for more
sensitive areas within urbanized zones and areas more susceptible
due to low-water crossings.

Kleebauer


Day 2
Valid 12Z Tue Apr 29 2025 - 12Z Wed Apr 30 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS INTO THE MISSOURI VALLEY...

The combination of favorable buoyancy and upper level dynamics
within the confines of a quasi-stationary front across the Southern
Plains to Mid-Mississippi Valley will create an environment
conducive for locally heavy rainfall over an area still recovering
from previous heavy rain episodes. Models are in agreement on the
placement of a west-southwest to east-northeast oriented stationary
front extending from the Western Rolling Plains of TX up through the
Red River Basin, bisecting much of central and northeastern OK, up
through the Ozarks of MO. Multiple mid-level shortwaves will eject
northeast out of MX creating a multi-wave convective initiation
cycle that will eventually move over the same areas repeatedly
during the course of the D2 time frame. Instability markers are very
favorable within the axis denoted above with sufficient buoyancy
on the order of 1500-3000 J/kg of MLCAPE situated across West TX to
points northeast through the Red River into OK. Assessment of NASA
SPoRT soil moisture anomalies pinpoint a fairly large area of
well- saturated top-layer soils running upwards of 90-98th
percentile across southwestern OK up into the Norman/OKC metro
corridor thanks to a significant flash flood episode that occurred
less than 36 hrs prior. Further northeast, soils are still
recovering from multiple rounds of convection the past several days
with elevated top-layer soils also running high within the 75-90th
percentile across the Tulsa CWA up through southwestern MO.
Considering guidance privy to these areas also being the
beneficiary of multiple convective rounds over the course of
Tuesday into Wednesday, there is a growing necessity for a higher
risk level forecast in these zones. Ensemble bias corrected
guidance has steadily increased the areal QPF averages from run to
run within these confines of northeast OK up through western MO, a
testament to the growing consensus in the heavy QPF footprint.

00z CAMs are only within the initial 12 hrs. of the period in
question, but the signs even prior to the bulk of the heavier
convective signature (Heaviest after 00z/29) are very much favorable
for potentially significant flash flood prospects. 00z HREF 6-hr FFG
exceedance probabilities for the 18-00z time frame are already
between 15-30% on the initial stages of heavier precip across the
Red River Basin of North TX into Southwestern OK up through Central
and Northeast OK. This is very likely due to the convective episode
stemming from the first mid-level shortwave ejecting northeast
generating a period of convection during the afternoon hrs. on
Tuesday. By Tuesday evening, large scale ascent will increase
substantially over the Southern Plains a potent mid-level shortwave
pivots over NM with a robust diffluent signature present downstream
into West TX and the adjacent Red River Basin. At the surface, a
cold front will motion south through the High Plains with an
expected convergence pattern developing as it moves into the already
present quasi-stationary front in place across the region. The
combination of the evolving surface and upper pattern will yield a
robust convective footprint across the Southern High Plains of TX up
through the Red River Basin, pressing northeast given the steering
pattern aloft. The episodic nature of the heavy precip will garner
limited recovery for areas already impacted by one round of
thunderstorms earlier in the period leaving a better opportunity for
flash flooding potential for the nocturnal period. There's some
discrepancy on exact placement of the more prolific convective
cores, but the one constant is the area expected to see the threat
is generally pinned down at this lead.

After coordination with local WFOs over North TX through OK,
Southeast KS, and Southwest MO...the previous MDT risk was expanded
to include much of Central and Northeast OK up through Southeast KS
into Southwest MO. A large SLGT encompasses areas surrounding the
MDT risk with areas like the eastern Permian Basin, Concho Valley,
and the Southern half of MO (Excluding the MDT risk area) within the
SLGT corridor. A broad MRGL extends from the rest of the Permian
Basin all the way through the Central and Northern Ohio Valley into
Northwest PA and far Southwest NY state as scattered convective
clusters will have the opportunity in these zones to produce locally
heavy rainfall capable of isolated flash flood prospects.

Kleebauer


Day 3
Valid 12Z Wed Apr 30 2025 - 12Z Thu May 01 2025

...THERE IS A MODERATE RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE ARKLATEX, EASTERN OKLAHOMA, AND WESTERN OZARKS...

The evolving upper air pattern along with the slow progression of a
cold front will yield another period of significant rainfall within
the confines of the Southern Plains to points east into the ArkLaTex
and Lower Mississippi Valley. Strong mid-level vorticity maxima will
translate eastward around the base of a potent mean trough
traversing the center of the CONUS. At the surface, a cold front
will be propagating eastward into the above corridors with ample
convection situated along and ahead of the front as it maneuvers its
way east. By the afternoon period Wednesday, sufficient diurnal heat
flux from typical daytime heating will provide ample instability
along and east of I-35 with a very buoyant forecast sounding being
depicted from multiple deterministic outputs, including the global
scale models, a testament to a pretty agitated environment. Above
normal PWATs on the order of +1 to 2 deviations coupled with a
textbook boundary layer convergence pattern will yield a swath of
heavy thunderstorms extending from Central TX to points northeast
into the vicinity of the ArkLaTex up through northwestern AR.
Latest deterministic output is between 2-4" on an areal average
basis with local maxima between 5-8" pending model depiction.
Ensemble means are generally between 2-3" for the period with the
bias corrected mean closer to 3-4" across the ArkLaTex up through
the western Ozarks, a signal that usually precludes a "ramp up" of
the precip depiction once we get closer to the range of the CAMs
guidance. Area soil moisture anomalies are once again fairly wet
across portions of eastern OK up into northern AR, leading to a
lower FFG parameter to meet for flash flood potential. Rainfall
rates will be between 1.5- 3"/hr during cell peaks, enough of a
signal to induce flash flood prospects even into northeastern TX
where soils are drier compared to areas further north. The D2-3
total QPF is now between 3-6" over the above areas, a defined
corridor for waves of heavy rainfall anticipated.

In coordination with local WFOs across OK, AR, TX, and MO...a MDT
risk was introduced to cover for the expected heavy rain threat over
areas anticipated to see significant convective impacts for
Wednesday into Thursday morning. Future updates will be provided as
we move closer to the event as later CAMs integration for the
forecast will provide better detail on forecast QPF maxima
placement, as well as magnitude.

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