Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
850 PM EDT Sun Sep 13 2026
Day 2
Valid 12Z Mon Sep 14 2026 - 12Z Tue Sep 15 2026

...THERE ARE SLIGHT RISKS FOR EXCESSIVE RAINFALL OVER PORTIONS OF
THE MIDWEST & SOUTHWEST...

2030Z Excessive Rainfall Discussion...
In the Upper Midwest...models tended to agree on the orientation
and placement of the axis of heaviest rainfall extending
northeastward from Nebraska/Iowa. However...within that axis there
was disagreement as to how far north or south. The CMC/UKMET placed
the heaviest rainfall in northeast Iowa or nearby
Minnesota/Wisconsin while the ECMWF/NBM and latest WPC
deterministic QPF aligned farther southwest. Either camp of
solutions fit within the previously-issed Slight risk area so left
the area unchanged. The Southwest US still looks to become active
once again with the model precipitable water and QPF fields
comparable to their previous solutions.

Bann

Previously issued Excessive Rainfall Discussion...

...Midwest...

A strong closed 500mb low, sporting 500mb heights below the 10th
climatological percentile per ECMWF, will work in tandem with a
strong 500mb ridge over the Mid-South to produce an exceptional IVT
throughout much of the North Central U.S.. The ECMWF SATs show the
IVT topping 1000 kg/m/s over the MO River Valley and into MN
Monday morning, then strengthening to >1,250 kg/ms/s over the
Upper MS Valley by Monday evening. These values are approaching
levels that could challenge the highest observed IVTs for mid-
September in the CFSR database (1979-2009), thus showcasing the
remarkable moisture transport at play. Strong theta-e advection
and anomalous PWs exceeding the 99th climatological percentile
will set the stage for an active day, consisting of widespread
showers and thunderstorms that contain highly efficient warm rain
processes.

The area of greatest concern is along the warm front,
closest to the surface low track, as veering low-level wind
profiles ahead of the approaching cold front support clusters of
organized thunderstorms. Latest WPC QPF shows widespread 1-2" of
rainfall from eastern NE to as far north as the Upper Great Lakes
with localized totals surpassing 3" possible. The inherited Slight
and Marginal Risks remain in good shape, but extended the Slight
Risk into southern NE to account for recent south and west trends
in QPF.

...Southwest...

Broad upper-level troughing over the West and upper-level ridging
in the Southeast will continue to support a healthy monsoonal flow
into AZ/NM and as far north as the Central Rockies. NAEFS shows IVT
values still topping the 90th climatological percentile for mid-
September. PWs will also surpass the 97,5 percentile for much of
eastern AZ and western NM. In addition, the Four Corners region is
ideally placed beneath the right- entrance region of a 250mb jet
streak that favors healthy upper- level ascent. The region has
remained fairly active in recent days and will continue to see
additional scattered showers and storms on Sunday, helping to
further saturate soils ahead of Monday.

QPF has trended wetter over eastern AZ and western NM, and given
soils are more likely to moisten rather than dry out in the coming
days, the Slight Risk was expanded to include more of southeast AZ
and far western NM. A broad Marginal Risk accounts for the
potential of localized flash flooding from central AZ on east
through much of NM and northward into the CO Rockies.

Mullinax


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