223
ACUS02 KWNS 131731
SWODY2
SPC AC 131729

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1229 PM CDT Sun Sep 13 2026

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM SOUTHEAST
NEBRASKA INTO WESTERN IOWA...

...SUMMARY...
Scattered strong to severe thunderstorms may impact parts of eastern
Nebraska into western Iowa late Monday afternoon into early evening.

...Discussion...
A mid-level trough will move across the northern Plains on Monday
with a strengthening 60-70 knot mid-level jet streak. The surface
pattern will feature a surface low across the Canadian Prairies and
a secondary weaker surface low across the central Plains. A moist
airmass will advect northward to the east of the surface trough with
mid to upper 60s dewpoints advecting into Nebraska and Iowa.

Thunderstorms will likely be ongoing at the beginning of the period
across eastern South Dakota and Minnesota into Iowa amid moderate
isentropic ascent. In the wake of this morning activity, northward
recovery will occur across northeast Kansas into southeast Nebraska
and southwest Iowa. Within this zone, a narrow period of favorable
conditions is forecast to develop ahead of front from southeast
Nebraska northward. Most guidance shows storms developing within an
environment featuring 2500+ J/kg MLCAPE and 30 to 35 knots of
effective shear during the afternoon. This would support a supercell
storm mode. If this discrete storm mode can be maintained, a EF2+
tornado threat will exist given the nearly purely streamwise
vorticity in the lowest 2km from RAP forecast soundings in the
region. Limiting factors to this scenario are multiple storms
developing along the front and quickly growing upscale and a lack of
strong venting flow aloft which may result in disruptive downbursts
before a more organized, strong low-level mesocyclone can develop.

Farther southwest, moderate instability and strong heating/lapse
rates may support isolated damaging wind gusts. Some guidance shows
~30 knots of effective shear which could support some marginally
rotating storms. If this occurs, some isolated large hail may be
possible. The 5% hail probability has been extended southwestward to
account for this threat.

Elevated thunderstorms will persist into the overnight period across
southern Wisconsin and northern Illinois within a strong low-level
jet and isentropic ascent. However, only modest elevated instability
and limited cloud-bearing shear should preclude much severe threat
farther east into southern Wisconsin and northern Illinois.

..Bentley.. 09/13/2026

$$