FOUS30 KWBC 230825
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
425 AM EDT Tue Sep 23 2025

Day 1
Valid 12Z Tue Sep 23 2025 - 12Z Wed Sep 24 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHERN
MISSOURI, FAR SOUTHEAST KANSAS, EASTERN OKLAHOMA, FAR NORTHEAST
TEXAS, ARKANSAS, WESTERN TENNESSEE, WESTERN KENTUCKY, AND SOUTHERN
ILLINOIS AND SOUTHERN INDIANA...

...Lower Arkansas Valley, Lower Mississippi Valley into the Lower
Ohio Valley...

The strengthening low level southerly flow/anomalous 850-700 mb
moisture flux that have supported organized convection over the
Central to Southern Plains early Tuesday will continue to support
the downstream push of this organized convection post 1200 UTC,
with these anomalous 850-700 mb moisture flux values of 2-3+
standard deviations above the mean moving from the eastern sections
of the Southern Plains into the Lower AR Valley, Lower MS, TN and
OH Valleys. There continues to be some north south spread in the
models with respect to the position of the max precip axis.
Generally, the non-CAMs are farther north and the CAMs farther
south. WPC continues to support the farther south qpf solutions,
with our day 1 risk areas drawn toward them. Overall, not a lot of
changes to the previous slight risk areas. We did extend the slight
risk farther east into the Lower OH Valley where there is expected
to be overlap of day 1 heavy precip with observed precip over the
past 24 hours. We also extended the slight risk area farther south
into northeast TX where several of the new 0000 UTC hi-res runs and
subsequently the new HREF mean show heavy precip. Otherwise, the
slight and 25% areas fit well with where the HREF and RRFS
neighborhood probabilities are high day 1 for 2" and 3+ amounts.

...Coastal Central California...
There continues to be good model agreement with the nearly
stationary closed low off the Southern CA coast beginning to
slowly move back to the north on day 1 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 coastal
Central CA, with values as high as 3-4 standard deviations above
the mean. With good model agreement on the closed low track day 1,
there is also good agreement on potential for areal average
moderate precip totals, with potential for locally heavier amount
along the Central CA coast. Isolated runoff issues are possible,
especially over any burn scars.

Oravec


Day 2
Valid 12Z Wed Sep 24 2025 - 12Z Thu Sep 25 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS THE
TENNESSEE AND OHIO VALLEY REGIONS...

Anomalous PW and 850-700 moisture flux values will stretch across a
large area from the Lower MS Valley, and into the TN & OH Valleys,
Central Appalachians and the Mid-Atlantic, ahead of the amplifying
longwave trof stretching from the Great Lakes, southward into the
Lower MS Valley. There still is a fair amount of qpf spread with
the max axis day 2. WPC is leaning more toward the multi model
ensemble qpf mean/NBM to drive our qpf and excessive rainfall
axes. This will support a widespread axis of moderate to heavy
precip amounts from eastern TX into the Lower MS Valley, TN and OH
Valleys.  While a large portion of the day 2 QPF and ERO axes are
currently in moderate to severe drought, there may be overlap in
qpf areas from day 2 and what has fallen over the past 24 hours
from eastern TN into central to eastern KY, and the Upper OH Valley
region. The previous slight risk was narrowed to better fit this
potential overlap areas. The marginal risk was also trimmed
significantly from southern L.P. of MI, IL, southeast MO and AR to
better fit the latest qpf update.

...Central California...
The slow moving closed low approaching the central CA coast late
day 1 will continue to push slowly eastward day 2 and push inland
by early Thursday morning. Similar to the day 1 period, an axis of
anomalous PW values, 2 to 3 standard deviations above the mean,
will persist to the east northeast of the closed low across Central
CA. Scattered convection in this anomalous PW axis will support
locally heavy rains across Central CA and isolated runoff issues,
especially across burn scar regions.

...Far southeast Arizona into New Mexico...
No changes made to the previous marginal risk area across this
region. Scattered convection possible, with localized heavy rain
and isolated runoff issues, especially in burn scar regions.

Oravec


Day 3
Valid 12Z Thu Sep 25 2025 - 12Z Fri Sep 26 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS SOUTHEAST
ARIZONA AND FAR SOUTHWEST NEW MEXICO...

The slow moving closed low moving inland into Central CA day 2 will
drop back to the south southeast toward Southern CA day 3. This
system will continue to have an area of anomalous PW values in the
vicinity of the upper center across Central CA into the Great
Basin. This closed low will also begin to tap anomalous PW values
over northwestern Mexico, transporting them into southeast Arizona
day 3. Model consensus is for a max precip area over Southeast
Arizona and far southwest New Mexico. The previous slight risk
across this area was only modified slightly, expanding it slightly
to the north and east to cover the model max qpf spread. Only some
minor changes to the marginal risk to the northwest of this across
northern AZ, southern NV, far southwest UT and into the central
Sierra. Locally heavy rains and isolated runoff issues possible
across these areas, especially over burn scars.

...Southern to Central Appalachians...
There will continue to be a broad axis of above average PW values
pushing eastward day 3 ahead of the elongated upper trof
stretching from the Great Lakes into the OH and TN Valleys. There
is a lot of qpf differences in this high PW axis, leading to low
confidence in where to put risk areas. Much of the eastern U.S. is
in drought conditions with low relative soil moisture levels. One
exception is over portions of the Southern to Central Appalachians
from eastern TN/far western NC/far southwest VA and eastern WV.
Kept the day 3 marginal confined to these areas and removed the
broader marginal from the previous issuance that extended north and
east into the Mid-Atlantic and southwestward to the Gulf Coast.

Oravec
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