Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
351 PM EDT Wed Apr 1 2026

Day 1
Valid 16Z Wed Apr 01 2026 - 12Z Thu Apr 02 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL STRETCHING FROM
CENTRAL OKLAHOMA INTO NORTHERN MISSOURI AND THE CONCHO VALLEY...

...Central to Southern Plains...

16Z Update: The previous forecast remains on track with a heavy QPF
signature focused within the warm sector of a maturing synoptic
pattern as a lee surface low migrates eastward through the Central
Plains. Latest 12z HREF neighborhood probabilities for >3" remain
very elevated (50-70%) across areas of southeast KS up into
west-central MO, coincident with the axis of greatest convergence
where a propagating cold front will couple with a budding LLJ and
maximized mid-level forcing to create a solid area of heavy
convection beginning this afternoon, carrying through the overnight
hours. Heavy rain signature remains most prominent between the
quadrant of I-35/44/49/70 with portions of both the Wichita and
Kansas City metros in mix for heavy precipitation. Backed flow for
a time across zone will allow for some training elements prior to
the precip field migrating east-northeastward as a frontal passage
finally puts an end to the setup. Overall, this setup has
relatively good continuity in guidance going back to a few days
ago, thus only minor adjustments were made to the overall SLGT risk
area with the "biggest" change being more of an extension eastward
through MO for areas along and north of I-70 to correlate with some
overlap of heavy precipitation over areas that saw heavy rainfall
the past 12hrs.

Kleebauer

..Previous Forecast Discussion..

The latest hi-res and global guidance noted a south/southwest-ward
shift of the axis of highest precipitation to central Oklahoma to
northern Missouri from its previous position of northeast Kansas
into east-central Iowa where areal averages of 1 to 3 inches are
expected. There remains a decent signal for localized 3+ inches in
the vicinity of the Topeka-Kansas City metros. The Slight Risk
area was adjusted to now cover eastern Oklahoma to northern
Missouri while the Marginal Risk was maintained from the Texas
Hill Country to the Mississippi/Ohio Valleys.

A prominent warm-sector will materialize from west-central Texas
into Missouri with a surface low forecast to be positioned over the
Central Plains by Wednesday afternoon. Several shortwaves will
eject northeast within and ahead of the mean trough leading to
multiple waves of rainfall from the south-central Plains into the
Middle Mississippi Valley. Some training potential, leading to 1-3
inch areal average amounts in this region, with some potential for
isolated higher amounts of 3+ inches. Farther south, a long axis
of convection is expected from Texas to Kansas along the cold
front, but storms in this area should be more progressive and soils
are even more dry than to the north.

Campbell/Santorelli


...Texas...

A SLGT risk was added across the Concho Valley in west TX as trends
for back-building convection along a well-established dryline will
open the door for heavy precipitation totals where training
convection is plausible. Recent HREF QPF trends were pretty
substantial in the last few cycles of the hi-res ensemble with the
blended mean QPF a solid 2-3" across the area between the Lower
Trans Pecos and points east-northeast to the northern fringes of
Hill Country. A lot of this setup stems from a sharpening dryline
that tilts back to the west-southwest as a maturing nocturnal LLJ
takes shape after 23z. Convergent signature within a favorably
unstable environment and stout 45-55kt bulk shear axis should allow
for the initiation of supercellular convective modes the first 2-4
hrs of any development followed by an eventual merger of cells as
the LLJ matures further. This is a classic scenario of the southern
edge of a larger ascent pattern in spring that tends to be more
appreciable for heavy rainfall with the dryline and LLJ convergence
zone becoming the focal point for where the higher QPF concerns
arise. Latest HREF neighborhood probabilities for >3" of rainfall
are between 40-60% with the bullseye centered over the Concho
Valley, including the San Angelo area where terrain and
urbanization factors lend credence to a better localized flash
flood risk for the area of interest. Hourly rate probabilities for
>1"/hr are very high (50-70%) for several hours across the same
area(s) which will be the driving force for the entire setup. In
coordination with the local San Angelo WFO, the SLGT risk was added
due to the evolving threat.

Kleebauer


Day 2
Valid 12Z Thu Apr 02 2026 - 12Z Fri Apr 03 2026

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

20Z Update: Evolution of the longwave pattern across the Central
and Northern CONUS will create a multi-round area of convection
over portions of the Midwest and Great Lakes beginning Thursday
morning with a second round expected by the evening hours. The
first batch of rainfall will be relatively appreciable, but rates
will be lacking due to a dearth in the overall instability fields
across the Great Lakes. Increasing southerly flow will aid in
advection of slightly warmer temperatures and increasing MUCAPE by
the afternoon which will act as a key ingredient for convective
development later in the day as large scale forcing shifts eastward
with a surface cold front approaching from the west adding to the
regional ascent pattern. 12z CAMs have shown inferences of heavier
rainfall bisecting some of the urban zones located over northern IL
into southern WI, extending northeast to western MI just over the
lake shore. There are relatively good probabilities >50% within the
HREF EAS fields for at least 1" of precipitation, but probabilities
for 2" are significantly lower within the same zones meaning there
is a general 1-2" mean QPF output from the latest convective
allowing models. This is also experienced within the latest bias
corrected ensemble forecast, a testament to the general range of
outcomes for this setup.

The primary area of interest for flash flooding will likely lie
over far northern Chicago suburbs up into the Milwaukee metro due
to the areal urban footprint and suggestion of heavier rainfall in
the area, especially the second round of convection. Fortunately,
rates are generally capped at 1-1.25"/hr at peak intensity with
much of the CAMs hourly outputs closer to 0.5-1"/hr for the
heaviest periods of impact. This lies right on the edge of any FFG
exceedance, so the threat will be somewhat capped overall for a
multitude of reasons. Decided to maintain general continuity from
the previous forecast with only minor adjustments on the northern
and southern peripheries of the inherited MRGL risk. Will keep an
eye on trends within the CAMs to see if a small upgrade is
plausible across the aforementioned area over northern IL and
southern WI, but in coordination with the local WFO's and current
setup, decided it was not worthy for the upgrade in the risk.

Kleebauer


Day 3
Valid 12Z Fri Apr 03 2026 - 12Z Sat Apr 04 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTHERN/CENTRAL PLAINS...

20Z Update: Only minor changes were made to the inherited SLGT risk
across the Southern Plains to Mid-Mississippi Valley as ensemble
output remains pretty consistent in the axis of where the heaviest
precip is expected for Friday evening into Saturday morning. High
1/3/6 hr FFG thresholds will likely subdue more appreciable risk
forecasts as a lot of rainfall will be necessary to approach more
substantial flash flood concerns, both magnitude and areal
coverage. That said, the longwave pattern and current forecast
instability would still be suitable for something bordering into
the higher end SLGT risk category, especially for central and
eastern OK down into the Red River Basin between the TX/OK border.
Will assess trends in the coming forecast periods to see if there
is any chance for changes, but right now the overall output from
guidance maintains a pretty solid run-to-run continuity with global
deterministic indicating perhaps a little more variance in
placement of heaviest precipitation corridors.

Kleebauer

..Previous Discussion..

Strong to severe thunderstorms along with embedded heavy rainfall
will track across the Southern/Central Plains into the 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. A Slight Risk was maintained and
adjusted to span from northern Texas to southwest Missouri.

Campbell


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