Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
834 PM EDT Thu Apr 2 2026

Day 1
Valid 01Z Fri Apr 03 2026 - 12Z Fri Apr 03 2026

...THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST AND MICHIGAN...

A couple of convective bands are moving across portions of northern
IL, southern WI, IN, and southern Lower MI. These areas have
pockets of 500-1500 J/kg of ML/MU CAPE and increasing CIN, with the
IN activity tapping the MU CAPE more than the ML CAPE. Effective
bulk shear has been sufficient for convective organization, and
precipitable water values have been 1.25-1.5". Should any cells
train or backbuild, 2" an hour totals would be possible in the very
near time.

Across much of this area, mostly due to recent rainfall, flash
flood guidance values are modest and these sort of rain rates
would be sufficient to cause issues. The mesoscale guidance
suggests that as the various forms of CAPE erode, much of the
activity should fade over the next few hours. There are mixed
signals as to whether or not activity in IL will backbuild or
reform southward, with the 18z HREF more emphatic about this idea.
This would fit RAP forecasts showing MU CAPE remaining a fixture
near the confluence of the MS & OH rivers while almost completely
eroding elsewhere overnight, which could allow for some convection
in and near southern IL to simmer overnight. Modified the existing
Marginal Risk to account for recent convective trends and this
idea.

Roth


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 AND MISSOURI VALLEY...

20Z Update: A powerful upper trough/ULL with an intensifying
surface low and trailing cold front will initiate quite the heavy
rain event across the Southern Plains up into the Missouri Valley
on Friday evening, carrying through Saturday morning and beyond.
Environment in both instability output and a deep moisture
advection regime across the Southern Plains extending into the
Ozarks and adjacent Missouri Valley will be prominent with PWAT
anomalies surging to 2-4 standard deviations above normal within
the broad warm sector centered over northern TX up into the Mid-
Mississippi Valley. Large scale ascent pattern is textbook for a
broad axis of maturing convection on the leading edge of the
approaching cold front with the western flank of the precip
situated along the cold front and a north-south oriented dryline
centered over west TX. The whole setup will slowly migrate to the
east as the upper level evolution gradually shifts northeastward
from the Northern Plains into the Upper Midwest leading to
relatively slow/modest storm motions capable of dropping copious
amounts of rainfall in a short period of time.

Strongest area of convergence is currently positioned where the LLJ
will combine with the cold front as the boundary tilts back
southwestward through TX, a classic scenario where heavy convection
is more apt to train for at least a short period of time. WPC 50th
percentile QPF across the area from North TX into eastern OK is
between 2-3.5" the 90th percentile well over 4" for a broad area,
including the DFW metroplex where flash flood concerns are always
relevant due to the sprawling urbanization factors leading to high
run off. 12z HREF neighborhood probabilities for >3" are between
40-80% across west-central TX to the Red River with 40-70% notable
as far north as northeast OK into northwest AR. The >5"
probabilities are between 20-50% across north-central TX, just
north of the DFW metro and encompassing portions of I-35 and areas
west. Dry antecedent conditions should prevent a more highly
impactful event as initial rain will be beneficial to the region.
However, the amounts being forecast in a span of 3-6 hrs as the
storms move overhead would be enough to cause problems with at
least a scattered flash flood prospects for where storms reach
those 2-3"/hr thresholds for a time. Considering the above, this
was more than enough to expand the SLGT risk further southwest into
the Concho Valley and even east into the I-35 corridor within proxy
of the DFW metro area. The area of eastern OK down into north-
central TX is classified as a higher end SLGT risk, outside a
higher risk category due to the very dry antecedent conditions
initially. Will be a time frame to monitor for any targeted
upgrades in these two specific areas.

Further north, convective development across eastern OK up through
the Ozarks and the I-49 corridor would be another area of interest,
mainly late in the period, as the cold front finally reaches this
area of the CONUS. Heavy rain from the previous periods over the
area south of the KC metro have dropped local FFG's to values
easily exceeded even in the more moderate thunderstorm outputs let
alone a more significant heavy rain depiction. HREF probabilities
for even >2" in the area run between 40-90% with the highest
probabilities located across southwestern MO, just outside the hard
hit areas referenced. Even so, the 3 and 6hr FFG exceedance
probabilities in that wetter antecedent environment are well north
of 60% in the latest HREF probabilities, a signature high enough to
warrant an expansion of the SLGT risk further northeast out of OK
and through the western Ozarks up through the I-49 corridor just
southeast of Kansas City.

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...

20Z Update: Very little has changed in the expected synoptic
evolution across the eastern half of the CONUS with a broad trough
and cold frontal progression likely to maintain incidences of
convection stretching from the Great Lakes/Midwest down into the
Mid-South and Southeastern U.S. The setup for flash flooding is
still very much contingent on the convective evolution that forms
upstream on D2, a tough task to engage in detail where variability
in convective behavior typically causes changes in the expected QPF
footprint and areal magnitudes forecast. As of now, the highest
risk is likely somewhere within proximity to the Southeastern U.S.,
namely areas along the Lower Mississippi Valley into MS/AL as the
frontal progression is expected to be within this zone around the
timing of the next nocturnal LLJ enhancement. An axis of
convergence between the front and LLJ will likely initiate a more
robust area of heavy convection capable of flash flooding,
especially in more urbanized zones. FFG's remain high overall
across much of the South, so the threat for more appreciable
impacts is low, but the setup could be enough to warrant a targeted
upgrade. For now, the MRGL was kept due to some of the uncertainty
remaining.

Kleebauer

..Previous Discussion..

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