Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
259 PM EDT Mon Sep 7 2026
Day 2
Valid 12Z Tue Sep 08 2026 - 12Z Wed Sep 09 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL OVER IOWA...

2030Z Update...

...Florida Peninsula...

Anomalous PWs up to 2.25" and a stalled frontal boundary will
utilize 1,000-2,000 J/kg of MLCAPE to trigger more scattered
thunderstorms capable of producing 2-3"/hr rainfall rates. The
setup is not too different than the setup that is supporting the
Marginal Risk for Day 1, but this time HREF/REFS members show
locally heavy rainfall rates could reside along the western coast
of FL. Slow storm motions with the aforementioned rates mentioned
above suggest the potential for a localize flash flood threat
Tuesday afternoon.

...Midwest & Southwest Marginals...

The Marginal Risks in the Midwest and the Southwest were merged to
account for an increase in WPC QPF over eastern CO and far western
KS. PWs are likely to surpass 1.25", which is above the 97.5
climatological percentile per ECMWF guidance, and a nearby frontal
boundary will help to generate thunderstorms in an environment
containing 500-1,000 J/kg MUCAPE. The QPF also increased along the
cold front in the Central Plains and Midwest, supporting an
expansion of the Marginal in those areas.

Mullinax

---Previous Discussion---

...Upper Mississippi Valley into the Upper Lakes...
The surface front pushing east into the Northern Plains day 1 will
remain very progressive day 2 into the Upper Mississippi
Valley/Upper Lakes. The progressive nature of the front will
continue to be a detriment to widespread runoff issues. However,
the southwestern portion of this front will slow somewhat compared
to the farther northern portion in the vicinity of eastern NE
/northeast Kansas, east into Iowa. Across these regions there is a
better chance of a period of training of cells late Tuesday/early
hours of Wednesday. This is shown in the latest guidance that has
consensus for a heavier axis of qpf here. A small slight risk area
was added across portions of central to southern Iowa for this
training potential. RRFS neighborhood probabilities are fairly high
for 1 and 2"+ amounts across the slight risk area, with a smaller
50%+ probability for 3"+ amounts over east central Iowa.

Marginal risk areas

..Eastern Arizona into western to central New Mexico...
No significant changes day 2 to the axis of above average PW
values extending from eastern portions of Arizona into western to
central New Mexico. Continued low confidence with qpf details, but
potential for another round of widespread scattered convection
across this area. Locally heavy rain and isolated runoff issues
again possible. Anomalous PW values also expected to push farther
north from Southern CA into Central CA. At the moment, models are
not showing precip developing day 2 in this anomalous axis.

The previous marginal risk area over northeast Montana was removed
given latest model qpf consensus. The broad marginal was also
removed along the Gulf coast into FL given less organized precip
than day 1

Oravec


Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt