Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
426 AM EDT Mon Sep 7 2026
Day 1
Valid 12Z Mon Sep 07 2026 - 12Z Tue Sep 08 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR A PORTION OF
NORTHWESTERN MONTANA...

...Northwest Montana...
A well defined shortwave expected to rotate northeastward from the
Northern Rockies into the Northern High Plains Monday. Model
consensus is for the development of a comma head/deformation precip
band to the northwest of this feature across northwestern portions
of Montana. There will likely be a period when this comma
head/deformation band pivots over northwestern Montana, supporting
heavy precip totals. The slight and marginal risk areas across this
area were changed slightly from previous issuances to align better
with the latest HREF and RRFS neighborhood probabilities for 1 and
2"+ amounts.

Marginal risk areas

...Upper Mississippi Valley...
The height falls ejecting northeastward from the Northern Rockies
into the Northern Plains will strengthen the low level southerly
flow along and ahead of the associated frontal boundary, raising
PW values to 1.75-2.00"+. Overall favorable large scale conditions
will support potential for organized pre-frontal/frontal
convection over the Upper MS Valley. At the moment, this convection
should be very progressive, limiting the excessive rainfall
potential to marginal. No significant change made to the previous
outlook area across this region.

...Eastern Arizona into western to central New Mexico...
PW values expected to remain above average day 1 from eastern
Arizona into western to central New Mexico. Widespread scattered
convection possible in this high PW axis,supporting locally heavy
rains and isolated runoff issues.

...Northeast Florida into coastal Georgia and coastal southern
South Carolina...
An axis of above average PW values will persist day 1 from the
coastal Southeast into northeast FL. Both the HREF and RRFS
neighborhood probabilities are fairly high in this above average PW
axis for 2 and 3"+ precip totals. Not a lot of confidence in qpf
details, but potential for locally very heavy rains and isolated
runoff issues, especially in more urbanized areas. The previous
marginal risk was reduced along the northeastern Gulf coast to
where the HREF and RRFS probabilities are greatest.

Oravec


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