Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
342 PM EDT Mon Apr 13 2026

Day 1
Valid 16Z Mon Apr 13 2026 - 12Z Tue Apr 14 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
NORTH-CENTRAL TO NORTHEAST WISCONSIN AND NORTHWEST L.P. OF MICHIGAN...

16z update...
12z CAMs remain on track for an active thunderstorm environment
with potential training cells capable of 1.75"+/hr rates and
localized 2-3" totals. There remains continued latitudinal variance
in the overall solution suite with another slight southward shift
in the axis of heavy rainfall.

The shortwave exiting the northern High Plains and expanding right
entrance jet outflow dynamics will allow for strengthening of the
low level jet; that initial WAA elevated cells should develop along
a favorable west to east orientated line generally parallel to the
mean steering flow to allow for training cells. However, the
slightly stronger LLJ inflow and southward proximity to more
unstable/moist air will allow for initially severe probably
rotating updrafts in S MN to expand, grow up-scale to broader
clusters and remain capable to intersect with rainfall of those
initial WAA cells. However, stronger inflow and rotation of
updrafts could allow for increased southward propagation as
well,this may reduce some of that overlap maintaining situational
uncertainty, though given the highly saturated ground condition and
coordination with local forecast offices, have introduced a Slight
Risk of Excessive rainfall across north-central WI to northeast
WI.

Downstream into the L.P. of Michigan, the overall convective
complex will roll through the areas saturated by heavy rainfall
yesterday, overall intensity should be reducing along with
increasing forward speeds to limit rainfall totals. However, (near)
record wet early spring, including spots of 2-4" yesterday, grounds
are near or fully saturated that any rainfall will be converted to
runoff and possible flash flooding. As such, the Slight Risk
extends across Lake Michigan to encompass those areas most
affected.

Further south toward Chicagoland and across N IND, the 12z HRRR is
bullish for convection breaking the cap across N IL later this
evening with stronger convective cores expanding through
interaction with the LLJ allowing for a favorable environment for
2-3" rainfall due to training. While recently dry over the last few
days/week, the area also remains well above average in upper soil
saturation values, AoA 60%, combined with larger urban centers
prone to flash flooding including: Chicago, Gary, South
Bend/Elkhart and Toledo, have expanded the Marginal Risk to account
for this potential scenario.

Gallina


~~~Prior Discussion~~~
A Marginal Risk for excessive rainfall was maintained for this
period from eastern Minnesota to Lower Michigan. Although there was
a modest decrease in the neighborhood probabilities for >1" totals,
there still 20 to 40% across eastern Wisconsin and western
Michigan as a formidable LLJ and increasing convergence within a
progressing warm front could very well maximize the potential for
heavier precip. Some rivers and streams across the region have
ongoing minor flooding and any additional rainfall could speed up
snow melt.

Campbell/Kleebauer

Day 2
Valid 12Z Tue Apr 14 2026 - 12Z Wed Apr 15 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL ACROSS THE CENTRAL
L.P. OF MICHIGAN...

21z update...
...Great Lakes Region...
With the introduction of a Slight Risk across
portions of WI, MI for the current Day 1 period, the affects of
today's rainfall activity will likely result in changes and
adjustments to this forecast. The synoptic environment did not
change much with another leading shortwave/vorticity center lifting
out over the mean ridge in the Great Lakes region. This will drive
stronger confluence of the LLJ across Iowa to break out another
round of strong/severe thunderstorms Tuesday evening. Overall deep
layer steering flow and fairly orthogonal ascent over boundary
reinforced by day 1 thunderstorm activity should help to focus a
similar west to east (WNW to ENE) oriented axis of training
thunderstorms. Upper-level dual jet couplet will further enhance
up-scale growth to a broader complex to maintain through the
overnight period, likely tracking through areas along or just south
of the Day 1 activity. Still, most of the area remains at near or
above record spring rainfall and soils are fairly saturated, so
with cells capable of 1.5-2"/hr rates and localized totals of 2-3+"
suggest the placement of a Slight Risk of Excessive Rainfall
across portions of eastern WI and central MI (along and north of
I-94).

...Pecos River Valley through Southern Plains into Ozark Plateau...
Little change in expected evolution, storm mode across this area
with the new 12z suite of guidance. Isolated cells along the dry
line will be initially slow moving eventually locally expanding
into smaller clusters after sunset. High moisture, slow cell
motions may result in locally heavy rainfall 3-4", but will be
isolated to widely scattered in nature. As such overall coverage
suggests the Marginal Risk in place will suffice. The Marginal Risk
area is connected to the area of concern over the Great Lakes and
while there was some consideration of splitting the Marginal areas
north of the Ozark Plateau to the Iowa border, but the threat
remains non-zero and confidence is not that high on precise areas
to remove; just note the coverage will decrease northward along the
dry-line with best probability near the Lower Pecos and south-
central OK based on current guidance suite.

Gallina

Day 3
Valid 12Z Wed Apr 15 2026 - 12Z Thu Apr 16 2026

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM TEXAS TO
THE UPPER MIDWEST/GREAT LAKES REGION...

21z update...
The surface to mid-level environment remains very similar to the
prior 3 days, with a stark dry line extending from the Pecos River
Valley across the Southern Plains into the Upper Mississippi
Valley. The longer wave mid-level trough is starting to finally
ejecting northeast into the central Plains though weakening as it
progresses northward. The deep layer moisture axis and instability
shift slightly eastward. As such clusters of thunderstorm activity
with ample 1.5" Total PWats should result in rates up to 2"/hr and
localized totals over 3" resulting in widely scattered clusters
along/ahead of the main front, maintaining the need for the axis
of Marginal Risk from northeast TX across the Ozark Plateau.

Across the Great Lakes, overall moisture and instability will be
reducing compared to prior days with warm front (mid-level
confluence axis) continuing to drift further south across the
Great Lakes. This moves further from the hydrologically
sensitive/saturated areas of the northern Great Lakes region, but
multiple days of stronger activity (current D1 and D2 periods) are
likely to result in areas that will have saturated ground
conditions by Day 3. Currently, the best overlap and probabilities
for the most active convection on day 3 to be across NE IL across N
IND into S MI and a Slight Risk may be required; however, without
soil conditions becoming saturated yet, will hold off on
delineating a categorical Slight Risk at this time.

Gallina


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