Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
1149 AM EDT Thu Apr 2 2026

Day 1
Valid 16Z Thu Apr 02 2026 - 12Z Fri Apr 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
NORTHERN ILLINOIS, WISCONSIN AND MICHIGAN...

16Z Update: The overall setup and expected evolution remains
consistent from previous forecasts with the heaviest rainfall
expected to occur after 18z from eastern IA to points east and
northeast as the surface low slowly intensifies and carries north-
east from IA through southern WI. Warm front positioning this
morning showed a modest advancement north, verifying well with the
current CAMs output as the boundary begins pushing through northern
IL at this hour. Expectation is for a defined warm sector to
materialize across eastern IA, northern IL, and southern WI with
the northern periphery of the theta_E ridge centered between the
Wisconsin Dells to just south of Sheboygan. Any area south of this
delineation will be under a threat of scattered convection capable
of heavy rainfall with rates generally between 0.5-1"/hr with the
max likely capped between 1-1.5"/hr given the instability/moisture
depth present. Despite climatological anomalies of PWATs around 3
standard deviations above normal, this is still modest in the
context of more appreciable rainfall prospects since it's still
only the beginning of April.

The primary areas of focus will be those more urbanized zones
where run off potential is highest just due to the limited
absorption that can occur within the infrastructure. Milwaukee,
northern Chicago suburbs, and Madison are the prime targets when
assessing the 12z HREF neighborhood probs for >2" as percentages
are running between 40-70% from just north of the Quad Cities to
the northern suburbs of Milwaukee. HREF EAS is very aggressive for
at least 1" in that same broad area, however there is a precipitous
drop off in the >2" EAS meaning the maximum is likely capped
considering the short term training risk and then steady northeast
progression as the region experiences the cold front passage later
this evening.

Considering the above variables, the only changes made were an
adjustment further southwest with the risk into eastern IA to
account for some trends in CAMs showing more aggressive convective
development later this afternoon over this particular zone which
upped some of the neighborhood probabilities for totals reach 2".
The best chance remains across southern WI with the Milwaukee metro
the most likely location for FFG exceedance and flash flood
prospects.

Kleebauer


Day 2
Valid 12Z Fri Apr 03 2026 - 12Z Sat Apr 04 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN PLAINS INTO THE OZARKS REGION...

Strong to severe thunderstorms along with embedded heavy rainfall
will track across the Southern/Central Plains into the Mississippi
Valley/Midwest during this period. Moisture (with PWs over the
90th, perhaps 95th percentile) and instability are likely to pool
along and ahead of the associated cold front and produce widespread
convection. Storms likely beginning in the afternoon are expected
to get reinforced through the evening and night hours as a low
level jet picks up ahead of the cold front. Given that some of this
region has been drier, it will take awhile before there are
substantial flash flood concerns. Some of the highest amounts/rates
are likely to focus over parts of central and eastern Oklahoma
down into the Red River Basin between the Texas and Oklahoma
border. Consensus has areal averages of 1 to 3 inches while some of
the hi-res guidance is hinting at isolated maximums of 4 to 7
inches. Slight Risk area spans from north-central Texas to
southwest-southern Missouri.

Campbell/Kleebauer


Day 3
Valid 12Z Sat Apr 04 2026 - 12Z Sun Apr 05 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FROM THE CENTRAL
AND EASTERN GREAT LAKES SOUTHWESTWARD TO CENTRAL TEXAS AND THE
LOWER MISSISSIPPI RIVER VALLEY...

Much of the convection that evolves across the Marginal Risk area
on D3/Sat will depend on specific evolution of convective complexes
that originate from the central/southern Plains on D2/Fri. Although
those details are a bit uncertain at the time frame, general
consensus is that one or two MCSs will traverse the Mississippi
Valley/Mid-South early in the forecast period before convective
redevelopment occurs upstream along a composite outflow/cold front
during peak heating hours from central Texas to Mississippi. Areas
of training are likely if this pattern holds, with initiating
boundaries supporting deep convection eventually becoming more
parallel to steering flow aloft. Portions of this region may
require an upgrade to Slight in later outlook updates.

Farther north, convective coverage is far less certain -
particularly from Illinois to Ohio. Deeper convection south of
these areas could disrupt inflow/instability and lead to a minimum
in precipitation in these areas. Again - this regime is uncertain.

The primary reason Marginal was maintained for D3 from Illinois
eastward to New York State and West Virginia was soils/local
sensitivity. Soils are wetter with eastern extent from prior
rainfall and could still be sensitive to even moderate rainfall by
D3/Sat in a few spots.

Cook


Day 1 threat area: www.wpc.ncep.noaa.gov/qpf/94epoints.txt
Day 2 threat area: www.wpc.ncep.noaa.gov/qpf/98epoints.txt
Day 3 threat area: www.wpc.ncep.noaa.gov/qpf/99epoints.txt