530
FOUS30 KWBC 131950
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Sat Sep 13 2025

Day 1
Valid 16Z Sat Sep 13 2025 - 12Z Sun Sep 14 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
SOUTHERN HIGH PLAINS AS WELL AS FOR WESTERN NORTH DAKOTA AND FAR
NORTHEASTERN MONTANA...

16Z Update...

Overall, made mostly minor adjustments based on the 12Z hi-res
guidance and recent observation trends. The only larger-scale
adjustment was made to the Marginal Risk area over the Midwest -
removing the northwestern extent from southern Wisconsin and
Illinois. As the convection moves downstream, maintained a Marginal
Risk over portions of Indiana. Convection there is expected to
remain progressive. Therefore, not expecting any near-term,
widespread runoff concerns. However, a few of the hi-res members do
redevelop some training convection, producing a narrow corridor of
heavier amounts later this evening/overnight. But given that those
models do not have a good handle on the ongoing storms, confidence
is limited.

Pereira

Previous Discussion...

...Central High Plains through Southern Rockies/West TX...

Upper trough over the Great Basin this morning will continue
slowly eastward and take on a negative tilt, with a continued
influx of moisture (PW anomalies +2 sigma) into the Southern
Rockies and points northward. As the trough axis crosses the Four
Corners region around 00Z tonight, LLJ increase will support
convection over eastern NM late afternoon that will push into West
Texas in the evening. Storms may have enough forward speed to limit
flash flooding potential, but 00Z CAMs continue to show potential
for 1-4" amounts. Focused the Slight Risk outline further from the
previous shifts to the best ensemble agreement.

...Northern Plains...

Southerly flow through the column will maintain a surge of
moisture (PW anomalies +3 sigma / 1.50") into the Northern Plains
as weaker shortwaves race northward ahead of the main upper low
over MT. Recent CAM guidance still shows some east-west
displacement of heaver north-to-south QPF maxima, owing to small
differences in shortwave/sfc boundary interactions and any morning
convection. Maintained the Slight Risk outline over western ND but
the eventual QPE footprint will likely be much narrower.

...Northeastern Illinois and surrounding areas...

Shortwave diving southeastward out of Wisconsin this morning at
the nose of a jet streak will help organize a small area of at
least modest rainfall around the Chicagoland area that continues
SSE-ward this afternoon. Some 00Z CAM guidance remains rather
bullish with 2-3" amounts which may be enough to cause some urban
runoff issues.

...South Florida...

Frontal boundary will remain just to the southeast of Florida, but
precipitable water values will start the day around 2 inches.
Drier air will slowly work southeastward through the entirety of
the Peninsula by the end of the day, and have targeted the Marginal
Risk outline to around the urban areas between Palm Beach and
Miami.


Fracasso


Day 2
Valid 12Z Sun Sep 14 2025 - 12Z Mon Sep 15 2025

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL IN THE WESTERN DAKOTAS...

20Z Update...

Extended the Marginal Risk further south from the central Plains
into western Oklahoma and the eastern Texas Panhandle, where
convection is expected to develop during the afternoon/evening
ahead of a low level confluence axis and within a stripe of deeper
moisture. While not anticipating a widespread heavy rainfall
event, some models do indicate the potential for slow-moving or
backbuilding cells, resulting in locally heavy amounts and perhaps
isolated flash flooding concerns.

Otherwise, no significant changes to the previous outlook.

Pereira

Previous Discussion...

...Central and Northern Plains...

Upper trough exiting the Rockies will split off its southern
portion into an upper low over western Nebraska midday Sunday, with
southerly flow continuing across the Northern Plains (and ample
moisture -- PW anomalies still +2 to +3 sigma). This mid-level low
will lift northward and act as a focus for convergence toward the
nose of the sfc- based instability gradient just to the east.
Storms may repeat over the same area as D1, with the potential for
another 1-2"+ of rain. Maintained the Slight Risk outline here with
a broader Marginal Risk extending to the south where the guidance
shows potential for 2-4" of rainfall, but over areas with higher
FFG values (esp. the Sand Hills).

Fracasso


Day 3
Valid 12Z Mon Sep 15 2025 - 12Z Tue Sep 16 2025

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Pereira


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