Day 3 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0238 AM CDT Tue Apr 21 2026

Valid 231200Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
SOUTHERN MINNESOTA SOUTHWARD INTO NORTHERN OKLAHOMA...

CORRECTED FOR TEXTUAL CLARITY

...SUMMARY...
Severe thunderstorms will be possible from northern Oklahoma into
southern Minnesota on Thursday. Large hail to very large hail,
damaging winds, and a few tornadoes are possible.

... Synopsis ...

A complex convective setup is expected on Thursday as a broad,
long-wave trough remains anchored across the Western US. While the
initial/primary shortwave will be lifting northward into Canada, a
secondary, lower amplitude wave is progged to approach the Southern
Plains overnight Thursday into Friday. 

At the surface, a Pacific cold front and dryline will push eastward
into the Central Plains. A secondary surface low is forecast to
develop near the triple point in northwest Oklahoma/southwest
Kansas. This feature will serve as the southern extent of the more
organized severe threat, with a conditional threat southward along
the dryline. 

... Central Plains ...

Thunderstorms are expected to develop along an advancing cold
front/dryline across portions eastern Nebraska into western Iowa,
before expanding both north and south. MUCAPE values between
1500-2500 J/kg and deep-layer shear on the order of 30-40 knots will
support supercellular structures initially, but unidirectional
profiles may favor splitting supercells, storm interference, and a
tendency for upscale growth into one or more linear segments. While
a few tornadoes may be possible early in the convective evolution,
large hail and damaging winds should become the dominant threat with
time. 

... Southern Plains ...

Convective initiation along the dryline south of the triple point
remains uncertain due to stronger capping. However, any discrete
cells that manage to initiate will do so in an environment
characterized by MUCAPE values between 2000-3000 J/kg with 30-40
knots of vertical shear. This will be more than sufficient to
support supercells capable of very large hail.

A secondary wave should approach the region overnight Thursday into
Friday morning. Forecast soundings indicate a steepening of midlevel
lapse rates associated with this feature and a subsequent increase
in CAPE values. Depending on the evolution of thunderstorms during
the afternoon and evening, additional thunderstorms may develop
overnight. The severe potential of these storms is uncertain given
the overnight timing of the wave and increasing convective
inhibition. However, strong vertical shear would seem to support a
hail and wind threat.

... Northern Plains/Upper Mississippi Valley ...

As the cold front pushes into the more modest moisture and buoyancy
profiles across northern Minnesota, the severe threat should be
lesser than areas to the south. Still, proximity to the upper wave
should support at least some threat for wind with any thunderstorms
that develop.

..Marsh.. 04/21/2026

Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0359 AM CDT Tue Apr 21 2026

Valid 241200Z - 291200Z

...DISCUSSION...
... An active severe weather pattern is expected through much of the
forecast period ... 

Broadly cyclonic midlevel flow will persist through much of the
forecast period to the south of a closed upper low over
south-central Canada. This will place much of the Southern Plains in
westerly or southwesterly mid- and upper-level flow each day. At the
same time low-level pattern will support southerly flow from the
surface up through 850 mb across the same region. The result will be
an increasingly moist airmass to the east of a north-south dryline
across western Oklahoma and Kansas, and to the south of a remnant
west-to-east frontal boundary. 

Diurnal heating of this moist airmass will result in afternoon
MUCAPE values around 2000-3000 J/kg Friday and Saturday beneath
30-40 knots of vertical shear. Model guidance continues to show
several perturbations within the midlevel flow traversing the
Southern Plains on Friday into Sunday morning. The result will be
multiple rounds of severe thunderstorms. The exact location and
dimensions of these daily severe threats will likely be augmented by
the prior days' convection, but the overall pattern supports near
daily severe potential across much of the Southern Plains. 

On Sunday (Day 6) a stronger, yet compact, midlevel wave is forecast
to move northeast across Oklahoma. This wave is forecast to induce
cyclogenesis across western Oklahoma, which should act to sharpen a
dryline. To the east of the dryline, strong southerly winds will
support surface dewpoints increasing into the upper 60Fs to perhaps
low 70Fs. Diurnal heating of this airmass will result in MUCAPE
values nearing 4000 J/kg across central Oklahoma. Deep-layer shear
approaching 50 knots will overspread the region during the afternoon
as the main wave approaches. Although global models are struggling
to initiate convection along the dryline, pattern recognition would
support a significant severe weather threat Sunday evening. The lack
of model convective initiation results in enough uncertainty to
preclude the introduction of 30% unconditional severe probabilities.
All severe hazards will be possible on Sunday.

The severe threat will continue into Monday/Day-7 as the midlevel
low and surface cyclone translate east into the lower Mississippi
Valley. The severe threat may continue into Tuesday/Day-8 across
portions of the Southeast US, although numerous days of preceding
convection should use up the steep lapse rate reservoir to the west
resulting in too much uncertainty to introduce unconditional severe
probabilities at this time.