FOUS30 KWBC 090749
QPFERD

Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
349 AM EDT Wed Sep 9 2026

Day 1
Valid 12Z 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...

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 2
Valid 12Z Thu Sep 10 2026 - 12Z Fri Sep 11 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER THE UPPER OHIO
VALLEY INTO THE CENTRAL APPALACHIANS...

...Upper Ohio Valley into the Central Appalachians..
PW values 2+ standard deviations above the mean are forecast along
the west-east oriented frontal boundary sinking south through the
Ohio Valley, Central Appalachians and Mid-Atlantic region day 2.
The previous slight risk area was adjusted southward by
approximately 80-100 miles to fit the latest model qpf consensus
for potentially heavy rains. H85 flow parallel to this front will
support training potential and also enhance uvvs in the upslope
regions of the Central Appalachians.

Marginal Risk areas.

...Southwest...
A marginal risk area was continued over portions of the Southwest
for potential for local heavy rains and isolated runoff issues in
the continued axis of above average PW values forecast across this
area. A marginal risk was also added for the Transverse Range of
Southern California where the RRFS was showing neighborhood
probabilities as high as 45%+ for 1"+ totals.

...Lower OH Valley, Mid to Lower MS Valley into the Southern Plains...
A broad marginal risk area was maintained to the
southwest of the Upper OH Valley/Central Appalachians slight risk
area, extending into the Lower OH Valley, Mid to Lower MS Valley
and westward into the Southern Plains of OK and northwest TX.
Scattered convection likely along the surface frontal boundary
where PW values will remain high, 1.75-2.00"+, but with FFG values
high and confidence low with where convection may maximize, the
threat level was kept at marginal.

Oravec
 

Day 3
Valid 12Z Fri Sep 11 2026 - 12Z Sat Sep 12 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE LOWER
MISSISSIPPI VALLEY INTO THE TENNESSEE VALLEY AND SOUTHERN
APPALACHIANS, OVER THE UPPER MISSISSIPPI VALLEY INTO THE CENTRAL
PLAINS AND OVER PORTIONS OF THE SOUTHWEST AND SOUTHERN GREAT BASIN...

...Lower MS Valley, TN Valley into the Southern Appalachians...
Above average PW expected across much of the southeast quarter of
the nation from the Lower MS Valley, eastward across the TN Valley
and into the Southern Appalachians during day 3.   Models are
showing some trof amplification across this area, with broad upper
difluence in this above average PW axis supporting widespread
scattered convection. With low confidence in qpf details and high
FFG values across these areas, the threat level is kept at marginal.

...Upper MS Valley into portions of the Central Plains...
A surface front expected to push east southeastward across the
Northern-Central Plains into the Upper MS Valley day 3. Model
consensus is for potential of locally heavy rains along and ahead
of this front. The previous broad marginal risk was narrowed to fit
the latest qpf axis consensus.

...Southwest into the southern Great Basin...
Increasing westerly mid level flow on the south side of the
amplifying closed low over the Pac NW day 3 will help push the
primary anomalous PW axis over the Southwest eastward from the day
2 position, becoming oriented from Southeast CA, into Arizona and
northward into the Great Basin. While there are the typical amount
of model qpf spread in this type of flow regime at day 3, there is
general consensus for scattered convection in this anomalous PW
axis, 1 to 2+ standard deviations above the mean. Locally heavy
rains and isolated runoff issues possible, with low confidence in
any qpf details.

Oravec
$$
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