Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1147 AM EDT Wed Sep 9 2026
Day 1
Valid 16Z Wed Sep 09 2026 - 12Z Thu Sep 10 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM SOUTHEAST
KANSAS INTO SOUTH CENTRAL MISSOURI, OVER SOUTHEAST COLORADO, SOUTHEAST
ARIZONA AND FAR SOUTHWEST NEW MEXICO...

16Z Update..

Minimal changes were made in this update, other than minor
adjustments to the inherited MRGL risk areas in the Southwest and
an expansion of the MRGL in the Mid-West. Latest CAMs guidance
depict a progressive line of thunderstorms forming along a cold
front, which per the latest HREF/RRFS guidance will support 1"/hr
rainfall rates in the newly expanded MRGL Risk area over the Mid-
West. Given the consistency over the expected progression, the risk
level was kept as a MRGL. In the Southwest, a removal of the MRGL
over the Sonora Desert in Arizona and California was needed given
updated QPF guidance suggesting reduced precip chances, and a lack
of a solid QPF signal among the majority of guidance. Otherwise,
the previous outlook and discussion remain in good shape.

Blanco-Alcala

...Previous Discussion...

An axis of above average PW values, 2+ standard deviations above
the mean, expected along the surface cold front pressing generally
southeastward day 1 through the Great Lakes into the Northeast and
southward through the Mid Mississippi Valley and into the Central
Plains. The northeastern portion of the front moving across the
Great Lakes into the Upper Ohio Valley and Northeast will be very
progressive, limiting any widespread runoff issues. Widespread
moderate to locally heavy rains possible along and ahead of this
potion of the front, with the risk level kept at marginal given the
expected progression.

..Central Plains into the Lower Missouri Valley...
Slower movement of the frontal boundary expected from the Central
Plains into the Lower Missouri Valley/Mid Mississippi Valley where
it will become more aligned to the westerly mid to upper level
flow. Simulated radars from the CAMS show general agreement with
the potential for training of cells in a west to east direction in
the 0000- 1200 UTC Thursday time period. HREF and RRFS
neighborhood probabilities for 1, 2 and 3"+ totals remain high in
the slight risk area from southeast Kansas into south-central
Missouri. A small slight risk area was introduced over southeast
Colorado where there is consensus for potentially heavy rains where
low level easterly to southeasterly flow is expected to strengthen
in the early hours of Thursday. HREF and RRFS probabilities of 3
hourly precip exceeding FFG values are in a similar area over
southeast Colorado early Thursday, with probabilities as high as 30
to 40%+ in the 0600-1200 UTC Thursday period.

...Southwest...
No changes made to the coordinated slight risk area across
southeast Arizona into far southwest New Mexico. Additional
scattered convection likely in the above average PW axis. The
slight risk area continues to coincide well with where the RRFS
and HREF show max probabilities of 3 hourly precip exceeding FFG
values. The RRFS is more emphatic than the HREF with these
probabilities, with values as high as 45-60%, compared to the HREF
range of 15-30%. No changes made to remainder of the broad
marginal risk from the Sierra, southward into Southeast CA and
eastward across portions of AZ and NM.

...Southwest Florida...
A weak mid level wave pushing west across South Florida will help
enhance uvvs in the tropical airmass, PW values 2.00-2.25"+. A
marginal risk area was added for Southwest Florida where HREF and
RRFS neighborhood probabilities are high for 1, 2 and 3"+ amounts.
The HREF is more emphatic about heavy rains, showing probabilities
of 3 hour precip exceeding FFG values as high as 40-60% late
Wednesday afternoon. This heavy rain potential may lead to
localized runoff issues, especially in more urbanized areas.

Oravec


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt