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

Day 1
Valid 01Z Tue Apr 14 2026 - 12Z Tue Apr 14 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MIDWEST...

...01Z Update...
General thinking in terms of convective development and
propagation continues this evening, as the activity is now
beginning to exhibit more upscale growth from northwest IA-
southern MN into central-nothern WI. While, more sfc-based
convection expands across northwest IA, with CAPEs between
3000-4000 J/Kg per the latest RAP/SPC mesoanalysis. Convection
becomes more elevated with the forced ascent along and north of the
warm front, with a deep elevated mixed layer (EML) and MUCAPEs
still healthy between 1500-2500 J/Kg. Over time, the activity will
continue to grow upscale into an MCS, with some likely southward
propagation later tonight as the south-southwesterly LLJ
strengthens to 45-55 kt early this evening before veering
southwesterly. By midnight CDT, the latest RAP shows weakening
Corfidi Vectors (less than 10 kts), indicative of the strengthening
upstream propagation as the robust LLJ aligns with the mean
850-300 mb flow while also reaching/ exceeding the magnitude of the
mean deep-layer flow. This will favor a higher probability of
training convection overnight withing the Slight Risk area, which
was expanded southward into much of southeast WI, while also
upstream to include the activity expanding across southeast MN and
far western WI. Other adjustments to the Slight and Marginal Risk
areas were based on the latest trends in the CAM guidance,
including recent HRRR runs and 18Z HREF QPF exceedance
probabilities.

Hourly rainfall rates underneath the strongest cells (esp HP
supercells) will reach 1.75-2.25" within an hour. For further
information, please refer to the latest Mesoscale Precipitation
Discussions or MPDs 100 and 101, both valid until 0330Z.

Hurley


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