Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1134 AM EDT Sat Aug 8 2026
Day 2
Valid 12Z Sun Aug 09 2026 - 12Z Mon Aug 10 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF THE
UPPER GREAT LAKES AND UPPER MISSISSIPPI VALLEY...

...Upper Great Lakes & Mississippi Valley...

A series of disturbances moving eastward along the southern
periphery of a large upper low well into Canada will result in
multiple rounds of storms on Sunday across the Slight Risk area.
The first will be the remnants of an MCS that will start the day in
far southeastern Minnesota, and will then track south and east
along the Wisconsin/Illinois border. The storms in general should
be pretty fast moving, so it's unlikely too many flooding impacts
will be seen from this feature alone. However, what it will do is
prime the soils by moistening them up for the later round.

The second round will form at the nose of a developing low level
jet Sunday night. The storms will follow the greatest instability,
which will mean the storms will track southward. The should be
significantly slower moving, and much more widespread compared to
the first round earlier in the day. The widely scattered instances
of flash flooding associated with the Slight will be mostly
confined to this Sunday night period. Urban and small stream
impacts in and around Chicago and possibly Milwaukee and Detroit
are the most likely impacts.

...Marginals Elsewhere...

As on previous days, deep tropical moisture across the Southeast
will favor another round of afternoon showers and storms from
northern Mississippi into the southern Appalachians. Flash flooding
will likely be confined to areas where the storms are most
persistent (northern Mississippi), or where terrain helps funnel
the rainwater (southern Appalachians). Generally the storms, while
scattered, should be disorganized, so a Marginal was maintained for
now, though targeted Slights are certainly possible in the coming
days.

The monsoon will continue across the 4 Corners region on Sunday.
While a bit more widespread over the Southwest, most organized
convection will be very limited, so few changes to the inherited
Marginal Risk were needed.

Wegman


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