FOUS30 KWBC 210821
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
421 AM EDT Sun Sep 21 2025

Day 1
Valid 12Z Sun Sep 21 2025 - 12Z Mon Sep 22 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE VICINITY OF
THE KANSAS/OKLAHOMA/ARKANSAS/MISSOURI BORDER AREA...

...Central-Southern Plains into the Mid Mississippi Valley...
Additional shortwave energy will be diving east southeastward 
through the base of the mean trof centered through the Central to 
Southern Plains into the Middle Mississippi Valley. These height 
falls will help strengthen the low level west south west to 
southwesterly flow into a west to east northeasterly oriented low 
level boundary stretching from the Southern Plains into the Middle
Mississippi Valley. This will support another round of convection 
pushing east from central to eastern KS/OK into much of MO, 
northwest AR and central to Southern IL. A slight risk area was 
added in the vicinity of the KS/OK/AR/MO border area that has seen 
heavy rains over the past 24 hours and may see additional heavy 
totals later in the upcoming day 1 period. Otherwise, there were no
significant changes made to the previous marginal risk area, that 
continues to fit well with the latest axis of high HREF 
neighborhood probabilities for 1 and 2"+ amounts during the 
upcoming day 1 period. Across these areas, relative soil moistures 
remain very low, which should help mitigate runoff issues, at least initially.

...Southern California into Arizona...
The closed low initially off the Central California coast will be
drifting only slowly southward day 1 to a position off the 
Southern California coast. A jet streak on the eastern side of this
upper trof will keep favorable right entrance region jet dynamics 
over Southern CA into Arizona. This will help accentuate lift in 
an axis of anomalous PW values, 1 to 3+ standard deviations above 
the mean that are expected to persist across these areas day 1. 
This should support potential for additional widespread scattered 
convection, locally heavy rains and isolated runoff issues.

Oravec


Day 2
Valid 12Z Mon Sep 22 2025 - 12Z Tue Sep 23 2025

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE  
CENTRAL TO SOUTHERN PLAINS, MIDDLE TO LOWER MISSISSIPPI VALLEY AND 
OHIO VALLEY AND ACROSS ARIZONA INTO WESTERN NEW MEXICO...

...Mid to Lower Mississippi Valley into the Ohio Valley...
The height falls pushing east southeastward day 1 into the Central
to Southern Plains and toward the Mid Mississippi Valley will 
continue to move eastward through the Ohio Valley day 2. Well 
defined large scale lift in an axis of above average PW values, 1 
to 1.5+ standard deviations above the mean, will support the 
likelihood of widespread moderate to heavy precipitation in an 
axis from northern AR, far southeast MO, far southeast IL, western 
to central KY, much of IN and OH. At the moment the convection 
across these areas may be fairly progressive. This and very low 
relative soil moistures, much of the area in moderate to severe 
drought, will keep the risk level at marginal for the time being. 
With respect to changes to the previous issuance, the northern edge
of the marginal risk was trimmed to the south by about 50-75 miles
to account for the latest model consensus.

...Central to Southern Plains...
The marginal risk area from the previous issuance was expanded 
slightly westward into western KS to cover the model spread with
the next round of convection forming ahead of the upstream
amplifying height falls dropping southeastward late 
day 1 from the Northern Rockies into the Central Rockies/Lee of the
Central Rockies on day 2. The GFS and NAM begin to diverge day 2 
with the track of this closing off mid to upper level center, with 
the NAM taking a more southeastward track into the Central Plains, 
while the GFS takes a more south southeastward track into the 
Central Rockies. The NAM solution, at the moment, is an outlier 
with the EC, UKMET and CMC more in line with the GFS. The
differing mid to upper evolutions have more of a qpf impact over
south central WY into north central CO, where the more southeast
NAM solution is much lighter than the remainder of the guidance. Do
not believe there will be any runoff issues farther northwest
across CO/WY given lack of instability. While models differ farther
to the southeast, there are still non NAM solutions that have
potentially heavy rains as far northwest as northwest KS day 2,
supporting the west northwest expansion from the previous issuance.

...Southwest...
The closed low off the Southern CA coast day 1 is expected to move
little on day 2. The right entrance region of the jet streak to 
the east of this closed low will push eastward from its day 1 
position, but continue to support uvvs enhancement in the above 
average PW axis, 1 to 3 standard deviations above the mean, that 
will remain in place across Southern CA into the Southwest. 
Additional scattered convection across these areas will support 
localized heavy amounts and isolated runoff issues. The previous 
marginal risk area was expanded westward into southeast CA to cover
the model qpf spread.

Oravec


Day 3
Valid 12Z Tue Sep 23 2025 - 12Z Wed Sep 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHERN
MISSOURI, NORTHERN ARKANSAS, NORTHEAST OKLAHOMA AND SOUTHEAST KANSAS...

There continues to be model differences in the evolution of the mid
to upper level trof over the Central to Southern Plains toward the
Mid Mississippi Valley. The NAM continues to be an outlier in being
more amplified and faster to push the height falls downstream.
Despite the differences, models do show re-strengthening of the low
level southwesterly flow ahead of surface low pressure moving east
across Oklahoma into Arkansas. This will support potential for
organized convection, that likely forms late day 2 to the north of
this low across the Central Plains, continuing day 3 from southeast
KS/northeast OK, across Southern MO and northern AR. Model
consensus is for the heaviest totals across these areas with
amounts of 2-4" possible. This heavy axis will possibly overlap
where heavy rains have fallen over the past 24 hours and where 
additional heavy rains are possible during the day 1 period. There 
were no major changes to the slight risk area from the previous 
issuance. The marginal risk was extended farther westward into 
northeast CO where several models show heavy rain potential day 3. 
The eastern portion of the marginal risk was also extended into the
Upper OH Valley to cover the model qpf spread. 

...Southern to Central California...
The nearly stationary closed low off the Southern CA coast day 2 
will begin to slowly move back to the north on day 3 toward the 
Central CA coast. This slow north movement will also allow for a 
northward expansion of the anomalous PW values over Southern CA 
into Central CA, with values as high as 3-4 standard deviations 
above the mean. There are differences with qpf distributions given
differences with the northward push of the closed low. Not a lot 
of confidence in any solution at this range, but continued 
potential for locally heavy rains and isolated runoff issues, 
especially over any burn scars. No changes made at the moment to 
the previous broad marginal risk area over Southern to Central CA.

Oravec
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