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

Day 1
Valid 01Z Mon Apr 13 2026 - 12Z Mon Apr 13 2026

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

...Texas...

01Z Update: Current CAMs are struggling with the handling of this
evening's QPF distribution with the best handle being maintained by
the RRFS, but even that is struggling a bit in the grand scheme.
Shortwave analyzed in Coahuila is still set to eject into TX
overnight with modest return flow off the Gulf anticipated for
areas of Hill Country to points east. Previous convection likely
maintained cold pool structure from earlier this afternoon, but
weakening convection overall should allow for boundary remnants 
to slowly shift north which is being seen via the convective
motions the past hour. A separate shortwave over north-central TX
will advance to the northeast during the evening with its own round
of convective enhancement leading to cells propagating into the
I-35 corridor mainly south of the DFW metro before moving into east
TX overnight.

The question becomes the potential convective initiation from the
LLJ coupled with the ejecting shortwave out of MX. Hedged towards
the maintenance of the SLGT risk from previous forecast as the
environment is ripe for heavy rates >2"/hr along with a remnant
boundary capable of a focal point for back-building. This SLGT is
relatively conditional for this evening, but what could form
certainly has the potential to be something more significant,
similar to what transpired earlier today with perhaps a little less
vigor due to a lower level of instability and relevant theta_E. A
MRGL extends around the periphery of the SLGT with a northern
extension close to the I-20 corridor near Dallas-Fort Worth.

...Great Lakes...

01Z Update: Scattered flooding due to a mess of hydrologic factors
across the Great Lakes will continue overnight with the best
opportunity lying east of Lake Michigan where a shortwave from the
southwest will migrate into the region with another round of
rainfall. Grounds across northern MI are becoming very saturated
with the snow/ice melt and the rainfall the past 24 hrs. Expect
this to continue through the evening with the next wave likely to
impact the eastern Lake Michigan shores from I-196 up to Traverse
City. The focal point will lie within that area over into the
northern mitt north of I-96. Additional totals of up to 1-1.5" are
possible this evening which could lead to isolated instances of
flash flooding and even more river flood concerns. The MRGL remains
in place for northern MI.

Kleebauer


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