Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
900 PM EDT Thu Jul 2 2026
Day 2
Valid 12Z Fri Jul 03 2026 - 12Z Sat Jul 04 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FOR MUCH OF IOWA
AND EASTERN NEBRASKA...

...2030Z Update...

Guidance has shifted notably south and west for the Day 2/Friday
period regarding where the heaviest rains are expected for the
period. Expect a dying overnight MCS to impact much of central and
eastern Iowa Friday morning, followed by renewed MCS development
Friday night starting in eastern Nebraska and continuing into
southern Iowa. The combination of these two areas of rain, with a
notable break in between, led to the shifting of the Slight south
and west of the inherited area, and the trimming of the Slight out
of areas east of the Mississippi River. Much of northern Iowa will
have seen 2 days of MCS's capable of producing heavy rainfall, so
the south and west shift of the heaviest rains is good news both
that the most intense areas of rain hit much drier areas soils-
wise, and that the hard hit areas of the state get lighter rainfall
over a longer time as outflow from the MCS' much heavier rainfall
to the south and west.

The heaviest rains for the day by far will come from a developing
MCS Friday evening through Friday night across eastern Nebraska
that tracks southeastward into south-central Iowa. It's in this
corridor that the more significant localized flash flooding could
occur, due to much heavier hourly rainfall rates.

Showers and storms will develop east from there through Chicagoland
and along Michigan's southern border through the day, but short
residence times of the heavy rainfall due to sufficiently fast
movement of the storms should keep any flash flooding risk in these
areas isolated and consistent with a Marginal Risk.

For southeast Florida, it will be a rinse and repeat scenario
regarding afternoon convection blossoming across the middle of the
state south of Lake Okeechobee, then slowly drifting east towards
the urban corridor from West Palm Beach south, where any isolated
flash flooding threat exists. A small Marginal Risk area was
introduced with this update.

Wegman

...Previous Discussion...

A similar pattern to day 1 (Thursday) will once again be in place
on Friday as the quasi-stationary frontal boundary remains draped
through the Upper Midwest under faster mean flow rounding the
eastern upper-ridge. Embedded upper-wave(s) will help to encourage
storm development with daytime heating. Seasonably high moisture
(PWATs 1.5-2") and instability (ML CAPE 3000-4000 J/KG) will also
continue to support robust storms capable of heavy downpours with
now-available hi-res guidance supporting locally heavy totals of
3-5". While the environment will remain primed for this additional
rainfall, there is greater uncertainty as to the exact
location/coverage of storms. Outflow from a potential MCS during
the day 1 period will help determine the location of the frontal
boundary on Friday. The hi-res guidance available through the day 2
period not surprisingly suggests the boundary will be further
south of where the global guidance depicts the corridor of heavier
rainfall. The inherited Slight Risk was adjusted following a more
east-west orientation that brought the eastern half of the risk
area south from central Wisconsin to include southern Wisconsin and
far northern Illinois. Additional southward adjustment may be
needed if these guidance trends hold but for now this at least
helps to orient the risk more similar to the east-west boundary
position/corridor of heavy rainfall suggested by the hi-res
guidance while still including the coverage of heaviest QPF in the
global guidance.

Putnam


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