ACUS03 KWNS 210739

SWODY3

SPC AC 210738



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



$$