Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Sun Apr 12 2026

Day 1
Valid 16Z Sun Apr 12 2026 - 12Z Mon Apr 13 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
CENTRAL AND SOUTHEAST TEXAS...

...Texas...

16Z Update: Conditions for a localized area of significant rainfall
are increasing as of the latest 12z CAMs and associated hi-res
ensemble with a QPF maxima positioned across the I-35 and points
just east to the I-45 corridor in eastern TX. Current radar
analysis shows a progressive line of thunderstorms migrating
eastward with a weakening disposition as of the last 30 minutes.
This set of storms will fade over the next few hours with a
secondary batch of cells likely to materialize to the southwest
across the I-35 corridor between Killeen to Austin on the edge of a
remnant cold pool from the aforementioned storms. Areal MUCAPE will
increase given favored diurnal instability leading to a widespread
area of 1000-2000 J/kg situated across the I-35 corridor and points
east with 2000-2500 a bit further back into Hill Country which will
lie within the western flank of any expected convective
development. Environmental parameters of shear and instability
along with a remnant cold pool will act as a favored initiation
point this afternoon with multi-cell modes and cold pool mergers
likely to enhance a more organized convective cluster across east-
central TX.

This first batch will have the ability to drop appreciable amounts
of rainfall with some of the CAMs insistent on QPF maxima between
3-5" on the first round of convective development with hourly rates
between 1-3"/hr in the stronger cell cores. Despite the drier
antecedent conditions in place, the overall hourly rates confined
within a narrow corridor would be sufficient to induce some
isolated to widely scattered flash flood signals within a region
that is prone to flash flooding due to the complexity of terrain
and unfavorable limestone bases that promote high run off
capabilities.

The real concern is what is being depicted in the evening as
another batch of thunderstorms is forecast to materialize within
the southern edge of a remnant cold pool from prior convection,
coupling with a weak LLJ developing across east TX after 00z. The
convergence pattern is well-documented across the area between I-35
to I-45 with a general overlapping in that zone from the latest
CAMs. Neighborhood probabilities for >5" total in the D1 period
have escalated to 30-45% across the above zone with a bullseye
centered between Austin/Brenham/San Marcos. Where this overlap
occurs with the previous round of convection, locally significant
flash flooding will be plausible considering the priming and totals
being represented in the means. HREF blended mean QPF is solidly
above 4" for multiple areas between the two major TX interstates
with some 5" pixels showing up over those areas east of I-35. The
SLGT risk in place has been expanded a bit further south to account
for these trends with the risk likely leaning towards the higher
end of the threshold. If the setup gains near term traction, a
targeted upgrade to a higher risk is not out of the question, so
this one will bear watching.

Kleebauer

...Great Lakes...

16Z Update: The MRGL risk remains in effect across northern MI, but
was expanded further west-northwest into the MI U.P. and northern
WI to adjust for the latest trends and observations of ongoing
rainfall and minor flooding taking shape in these areas. Secondary
batch of elevated convection migrating northeast out of
MN/southwestern WI will entice more localized hydrologic concerns
over the area where the coupling of snow melt and moderate to heavy
rainfall will enhance flooding of rivers and streams littered
across the northern Great Lakes. Some flood reports are trickling
in across the area already, so want to cover bases with a low-end
flash flood threat to mingle with the river flood prospects as
multiple rounds of convection are anticipated through the period.
The next batch will drive up from the south as a weak shortwave
enters from the central Midwest and provides another period of
convectively driven rainfall from south to north beginning in IA/IL
and moving northeast impacting parts of the Door Peninsula into the
northern mitt of MI.

Kleebauer

..Previous Discussion..

A Marginal Risk remains in effect for this period. Anomalous Gulf
moisture pumping northward will interact with the draped frontal
boundary to bring enhanced rainfall to the region. NAEFS continue
to show PWs and IVT values that are above the 99th climatological
percentile that features a combination of saturated soils and
lingering snowpack. Accumulations of 1 to 2 inches are anticipated
for the northern half of Mitten which may cause any lingering
snowpack to melt and possibly exacerbate the flooding potential on
Sunday.

Campbell/Mullinax


Day 2
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...

20Z Update: Little change was necessary to the inherited MRGL risk
across the Upper Midwest and Great Lakes. High neighborhood probs
(60-90%) for >1" totals across the region coupled with rapid snow
melt over the U.P. and northern WI should enhance hydrologic
concerns for the period. Minor flooding occurring in D1 will
generally continue through D2 as another round of convection will
impact the area from eastern MN through the northern half of MI.
There's some elevated probabilities for rates exceeding 1"/hr
across portions of WI tomorrow evening as a formidable LLJ and
increasing convergence within a progressing warm front could very
well maximize the potential for heavier precip. This would be the
most notable location for the setup, but the setup is relatively
short- lived, so did not feel an upgrade was necessary.

Kleebauer

..Previous Discussion..

Another round of showers and thunderstorms will move through the
Upper Mississippi Valley and Great Lakes during the afternoon and
evening hours, prolonging the threat for excessive rainfall,
increased snow melt and flash flooding. A Marginal Risk
remains in effect from eastern Minnesota to northern Michigan.

Campbell


Day 3
Valid 12Z Tue Apr 14 2026 - 12Z Wed Apr 15 2026

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FROM THE TEXAS
HILL COUNTRY TO THE UPPER MIDWEST/GREAT LAKES REGION...

20Z Update: The broad MRGL risk for D3 was generally maintained
with multiple areas likely to see convective activity during the
period. The main area of focus will likely occur over the Midwest
as increasing diffluent axis downstream of a deep western trough
will enter the area with convective development likely to occur
over IA and motion to the east-northeast. A developing upper jet
coupling will likely aid in regional ascent with fairly generous
instability axis situated from the Corn Belt to the southern Great
Lakes and points south. Models are in agreement on there being a
solid precip footprint, but they are all over the place in regards
to the placement. In any case, there was still some time to review
with the CAMs guidance coming into the picture by tomorrow, so will
wait to see if there will be another upgrade potential with this
setup, which is leaning more towards a necessity considering the
above synoptic and thermodynamic variables.

Kleebauer

..Previous Discussion..

Multiple rounds of strong to severe thunderstorms expected from
Texas to the Midwest states, given favorable wind shear and
instability in place as multiple impulses eject across the Plains.
Gulf moisture will be funneling northward between the trough over
the Rockies and the ridge over the eastern states. The environment
will be favorable for a few mesoscale convective systems to
develop and the limited eastward progression will likely result in
areas that have excessive rainfall leading to some instances of
flash flooding. A Marginal Risk area span from the Texas Hill
Country northeastward to the Midwest and western Great Lakes.

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