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

Day 1
Valid 01Z Sun Apr 12 2026 - 12Z Sun Apr 12 2026

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

...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

...Central Plains...

Guidance has struggled with the renewed convection along and s-sw
of the warm front across southern-central portions of KS, and
although there is some convective inhibition (MUCAPES trending down
over the past few hours), per the latest IR loops (streaks of
cooling cloud tops), additional organized clusters will maintain
the Marginal Risk area overnight into central portions of KS.

Hurley

...Upper Midwest and Great Lakes...

While still a non-zero threat, believe the 40km/25mi neighborhood
probability of rainfall exceeding flash flood guidance is less than
5 percent. Deep-layer instability is sorely lacking, as such are
rainfall rates, and even though there will be some uptick
overnight (elevated CAPEs climbing between 250-500 J/Kg), the
latest guidance trends, including 18Z HREF QPF exceedance
probabilities, suggest that the 1-3 hourly rainfall rates will
remain below FFG for the most part (i.e. likely >95% of the
activity).

Hurley


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