Excessive Rainfall Discussion
NWS Weather Prediction Center College Park MD
836 PM EDT Thu Apr 16 2026

Day 1
Valid 01Z Fri Apr 17 2026 - 12Z Fri Apr 17 2026

The probability of rainfall exceeding flash flood guidance is less
than 5 percent.

Bann


Day 2
Valid 12Z Fri Apr 17 2026 - 12Z Sat Apr 18 2026

...THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE MIDWEST, MID-MISSISSIPPI VALLEY INTO THE SOUTHERN PLAINS...

20Z Update: The synoptic evolution described in the previous
forecast has not changed in the latest model depictions as a broad
axis of heavy rainfall stemming from widespread convection is
anticipated from the Central Midwest down through portions of the
Southern Plains. The main change(s) from the previous forecast were
an expansion of the SLGT risk to the southwest, including more of
central and eastern OK, as well as an extension north to include
some of the more sensitive areas of southern WI and adjacent
northern IL/IN. The latest 12z HREF continues its trend on a slow
shift to the south with the areal QPF footprint signaling more
excessive rainfall prospects of 2+ inches now south of I-70 in MO
into more of northeast OK. This matches the ML suite from both the
EC AIFS and AIGFS outputs, both of which have been consistent in
their interpretations of heavier rain south of the global
deterministic suite the past few days.

Probabilistically, the trends have favored a particular zone
spanning the area between Kansas City to Tulsa along the KS/MO
border down through northeastern OK as the primary area of focus as
this zone nestles perfectly within the evolving upper jet coupling
that will materialize during the synoptic evolution occurring over
the Central and Southern U.S. Neighborhood probabilities of 50-80%
of at least 2 inches are located across portions of eastern KS into
west-central MO, overlapping an area of more sensitive grounds
after a heavy rain episode occurred over the area just north of
Springfield, MO this past evening. The overlap coinciding with
higher probs for at least 2 inches pin-points an area of interest
and is well-within the favorable environmental conditions that will
be in-place downstream of the approaching trough ejecting out of
the Rockies. Combination of deep moisture advection and suitable
instability noted by a strong theta_E ridge developing across the
Southern Plains to Midwest should promote relatively good rate
potential as probs for hourly rates remain very high for >1"/hr
(60-90%), and modest for even upwards of 2"/hr (15-25%) that would
easily exceed the hourly FFG threshold in place over the
aforementioned area. In this case, the SLGT risk would be deemed a
higher-end risk with a potential for even an upgrade if the trends
continue to favor that area of the CONUS seeing appreciable
rainfall tomorrow afternoon and evening.

Further north, the area encompassing the Central Midwest around
southern WI and northern IL remain in a more sensitive hydrologic
state due to the multi-wave convective episodes and upstream snow
melt aiding in swollen creeks and rivers throughout the region. The
impending setup would likely embrace a northern edge of heavier
precipitation based in the broad convective pattern materializing
over the course of Friday afternoon and evening. A strong mid-level
shortwave ejecting through the north-central Plains should allow
for a zone of rapidly developing convection across northern MO
through northern IL and southern WI after 19z as the frontal
approach likely enhances a convergence pattern over the area. This
should be enough to generate scattered thunderstorms across the
region leading to locally heavy rainfall over the saturated areas
referenced above. The combination of primed antecedent conditions
at the ground level and favored kinematic pattern have allowed for
an expansion of the SLGT risk further north to account for the
heightened threat given the recent trends in CAMs and associated
HREF QPF outputs.

Kleebauer

..Previous Discussion..

A deep, positively-tilted longwave trough advancing into the Plains
will promote broad areas of ascent from the Southern Plains to the
Midwest. A well-defined axis of diffluence ahead of the mean
trough with several shortwaves rippling through the flow will
enhance an area of convective development within a strengthening
warm-sector environment positioned between a strong cold front over
the High Plains and a quickly advancing warm front migrating
poleward through the adjacent Mississippi and Ohio Valleys. This
environment will be rather favorable for a broad footprint for
heavy rainfall. There has been a persistent south/southwest trend
with the axis of highest QPF for several model cycles which now
focuses over northeast Oklahoma to north-central Missouri with
areal averages of 1-2 inches with isolated maximums nearing 3+
inches.

Campbell/Kleebauer


Day 3
Valid 12Z Sat Apr 18 2026 - 12Z Sun Apr 19 2026

...THERE IS A MARGINAL RISK FOR EXCESSIVE RAINFALL FOR PORTIONS OF
THE SOUTH, LOWER MISSISSIPPI VALLEY AND TEXAS...

20Z Update: MRGL risk inherited was relatively unchanged across
MS/LA/Eastern TX as model guidance maintained general continuity in
the evolution of heavy precip likely developing along a convergence
axis situated along an approaching cold front from the north and
northwest. Totals seem consistent between 1-3" for the main axis of
development between the eastern edge of Hill Country in south-
central TX up into the Piney Woods area of southeast TX through
the Lower Sabine into southwest LA. This area has some of the
higher FFG's nationally, so the prospects for flash flooding will
likely be most coincident with more urbanized zones where run off
capabilities are highest. This would likely occur in the suburbs of
Houston and Lake Charles, along with a place like Beaumont where
urbanization is most prevalent.

The main change was a removal of the MRGL risk across south-central
TX to the Rio Grande where guidance, both deterministic and ML,
have reflected a relative min in QPF compared to areas downstream
along with high FFG's likely to thwart flash flood potential. In
coordination with the local WFO's accounting for the change, the
risk area was removed for the period.

Kleebauer

..Previous Discussion..

The frontal system described above will continue to advance
eastward with the trailing tail of the cold front dropping
south/southeast through Texas and the Lower Mississippi Valley.
Gulf moisture will be advecting northward into the Southern Plains
and pooling across Texas. PW values of 1.4-1.7 inches will be
present over much of eastern Texas and Louisiana during this
period. Strong convergence will lead to showers and thunderstorms
focusing along and ahead of the frontal boundary, especially for
the later half of the period. Areal average of 1 to 2 inches
expected with hourly rainfall rates greater than 1 inch/hr as well
may lead to isolated areas with flash flooding concerns. A Marginal
Risk area is in effect from South Texas to northern Mississippi.

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