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

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

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL FROM PORTIONS OF
TEXAS NORTHEAST INTO THE MID-MISSISSIPPI VALLEY...

...Oklahoma into western Illinois...
Recent mesoscale model guidance and radar reflectivity trends show
that continuity is generally on track, so changes to the previous
risk areas have been minimal. An elongating area of organized
convection extends ahead of a convective wave presently in western
OK up an existing frontal boundary, with convection showing slight
eastward movement. Hourly rain amounts to 2.5" have been seen due
to cell training, cell mergers, and embedded mesocyclones. Local
totals in the 4" range are possible in this environment where very
heavy rain can persist for 1.5 hours or so. The heavy rain
potential should continue into the early morning hours of Thursday
before fading by 12z.


...Central Texas...
A Slight Risk remains across the Concho Valley in west TX as
trends for convection running out ahead of a retreating dry line.
The atmosphere shows a favorably unstable environment and stout
45-55kt bulk shear axis should allow for the initiation of
supercellular convective modes shortly 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. Hourly rain
amounts to 2.5" with local totals to 4" are possible here as well.
Continuity could be well maintained, using the recent mesoscale
guidance as a guide.


...Upper Ohio Valley...
While convection appears to be on the wane in this area, the
mesoscale guidance suggests that some activity could continue to
bubble overnight. Local amounts in the 1-3" range occurred here
over the past 24 hours. Left the Marginal Risk in this region
intact as a course of least regret.

Roth


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