Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
315 PM EDT Sat Apr 11 2026

Day 1
Valid 16Z Sat Apr 11 2026 - 12Z Sun Apr 12 2026

...THERE IS A SLIGHT RISK OF EXCESSIVE RAINFALL ACROSS PORTIONS OF
THE SOUTHERN PLAINS...

...Central Plains...

The MCS responsible for periods of excessive rainfall and
resulting flash flooding will continue through the remainder of
this morning. The 12Z TOP sounding shows as much as 1,000 J/kg of
MUCAPE, along with a saturated and nearly 8,000ft warm cloud layer
aloft, plus a highly sheared environment featuring excellent low-
level SRH in the sfc-1km layer that exceeds 250 m2/s2. The ARW has
handled this complex the best, and its new 12Z run suggests
organized thunderstorms will linger for at least a couple more
hours over northeast KS and far northwest MO. WPC has issued a new
MPD, #0091, to highlight the ongoing flash flood threat. But with
several more hours of excessive rainfall expected, opted to
maintain the Marginal Risk until at least the 01Z update.

Mullinax

...Southern Plains...

Flash flooding is very much a concern from the Big Bend on north
and east through the heart of TX this evening and into tonight.
NAEFS shows anomalous IVT values over 500 kg/m/s (above the 97.5
climatological percentile) ahead of an approaching 200-500mb mean
trough axis. Current visible satellite paints a generally broken
cloud field over much of the state, although some surface based
heating should allow for up to 1,000 J/kg of MLCAPE late afternoon
and this evening. Storms initiating along the dryline will have a
favorable vertical wind profile that sports sufficient shear
(30-40kts of sfc-6km shear) and sfc-3km storm-realtive helicity
(SRH) >100 m2/s2. Any discrete cells initially should manifest
into a congealed cluster with some cells potentially training and
back-building north of the Rio Grande. The new 12Z HREF shows
pockets of moderate-to-high chances (50-80%) for rainfall totals
>3" from the Rio Grande to as far north as the Red River. More
concerningly, there are moderate chances (40-50%) for localized
totals >5" close to Del Rio, TX. While a moderate was considered,
ultimately held a Slight given the regions lower FFGs. However,
this is more of a "high-end" Slight, given the potential for
rainfall rates up to 2"/hr and the typical flash flood risks that
the TX Hill Country has a long history of enduring.

Mullinax

---Previous Discussion---

The presence of an increasing southerly low level will transport
Gulf moisture northward and pool over the Plains and Mississippi
Valley as an upper level trough enters the West and ridging builds
over the East. Meanwhile the upper dynamics and embedded shortwave
energy will support ascent ahead of a longwave trough. At the
surface, a dry line across West Texas will help serve as an
initiating mechanism for convection in the afternoon. Strong to
severe thunderstorms are expected to fire up over the Southern and
Central High Plains, migrating eastward eventually making headway
into the adjacent Concho Valley and lower Trans Pecos. As cells
merge due to cold pool mergers and low-level jet initiation, a
large cluster of heavy rainfall will ensue through the rest of
Saturday night into Sunday morning.

General consensus maintains 2-4 inches possible from the Concho
Valley in West Texas to the Red River Valley in southern Oklahoma.
Neighborhood 24 hr QPF HREF probabilities show a strong signal for
50-80% for 2 inches for this region and 40-70% for 3 inches. A
Slight Risk for Excessive Rainfall remains in effect across
portions of the Southern Plains, especially the areas referenced
above.

Campbell

...Upper Midwest and Great Lakes...

The Marginal Risk was expanded southward into southern WI,
northeast IA, and northern IL for the 16Z update. Latest ARW and
HRRR have trended south with their QPF axis with storms forming
closer to the lifting warming front. This setup has eerily similar
characteristics that led to the flash flooding in northeast KS
this morning; sheared lobes of 500mb vorticity to the west of the
upper-level ridge axis with area-averaged soundings showing
notable low-level SRH values and over 500 J/kg of MUCAPE aloft.
Warm cloud layers at least 8,000ft deep and NAEFS highlighting a
robust 750 kg/m/s IVT over central IA being aimed at southern WI
tonight also supported both warm rain processes and healthy
moisture advection. 1-hr FFGs remain as low as 1" in some locations
given the saturated soils in place. With these factors accounted
for, the Marginal Risk will focus on the potential for flash
flooding in these aforementioned areas tonight and into the early
morning hours on Sunday.

Mullinax

---Previous Discussion---

Scattered to widespread convection is expected across parts of
Wisconsin and Michigan as moisture increase along a warm front
lifting northward through the region. Areal averages of around 1
inch are still on track. Much of the region will be sensitive to
additional precipitation as there has been ongoing snow melt and
high river flows. Although it may be isolated, flash flooding
may be possible during this period. A Flood Watch remains in effect
across the Michigan U.P. and far northern Lower Michigan and
Wisconsin.

Campbell

Day 2
Valid 12Z Sun Apr 12 2026 - 12Z Mon Apr 13 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR CENTRAL
TEXAS...

...Central Texas...

Broad troughing in the west will continue to direct sheared 500mb
vorticity maxima at the Southern Plains as a narrow 250mb jet
streak over the Central Plains places its divergent right-entrance
region over central and southern TX. Between the trough in the West
and high pressure over the Southeast, a strong IVT exceeding 500
kg/m/s will engulf much of the Southern Plains with 1,000-2,000
J/kg of MLCAPE. Storms will form Sunday afternoon and continue into
Sunday night along and ahead of the dryline. Vertical wind shear
and low-level helicity will be sufficient to support strong-to-
severe storms, but the uncertainty lies in the orientation of
surface troughs and outflow boundaries that reinvigorate storms
Sunday night, and where they are located. Some CAMs show some more
progressive segments of storms, while others show potential for
back-building and training.

12Z HREF guidance, specifically 24-hr QPF probabilities, show
moderate chances (40-60%) for rainfall totals >2", with the bulk of
the rainfall coming after 18Z and before 12Z Sunday. There are some
low chance probabilities (20-30%) along I-35 from San Antonio to
Austin. Southern and eastern TX badly need rainfall (UNL drought
monitor shows severe drought in many places), but excessive
rainfall rates approaching 2"/hr over very dry/hard ground can
become hydrophobic. Add in the metro areas at risk (I-35 corridor)
and the inherited Slight Risk still looks to be on track.

The expansive area of anomalous moisture (>90th climatological
percentile per NAEFS) extends as far north as eastern OK, southeast
KS, and southwest MO. Excessive Rainfall in these areas will be
largely driven by the aforementioned 250mb jet streak as southerly
850mb winds inject the moisture into this divergent setup aloft.
Soundings are not as saturated and storm motions are faster, thus
supporting the Marginal Risk currently in place.

...Northern Michigan...

Gulf moisture will continue to transport northward and interact
with the frontal boundary draped across the region. NAEFS shows PWs
and IVT values that are above the 99th climatological percentile
over a region that features a combination of saturated soils and
lingering snowpack. An additional 1 to 2 inches of rain is forecast
across the upper portion of the Mitten,causing any lingering
snowpack to melt and possibly exacerbate the flooding potential on
Sunday. With little change in the forecast, a Marginal Risk for
Excessive Rainfall remains in effect across northern Michigan.

Mullinax

Day 3
Valid 12Z Mon Apr 13 2026 - 12Z Tue Apr 14 2026

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE UPPER MISSISSIPPI VALLEY AND UPPER GREAT LAKES REGION...

Following a brief lull in the action Monday morning, showers and
thunderstorms will return across the Upper MS Valley and into the
Great Lakes Monday afternoon and into Monday night. 500mb PVA and
jet streak dynamics will foster excellent vertical ascent within
the column at the same time another anomalous moisture plume
arrives ahead of a developing low pressure system. Additional
rainfall will prolong an elevated threat for flash flooding and
speed up snow melt around the region, most notably the U.P. of
Michigan. A Marginal Risk remains in effect from eastern Minnesota
to northern Michigan.

Mullinax

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