253 

ACUS03 KWNS 121932
SWODY3
SPC AC 121930

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0230 PM CDT Sun Apr 12 2026

Valid 141200Z - 151200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
THE SOUTHERN PLAINS TO THE GREAT LAKES...

...SUMMARY...
Isolated to scattered severe thunderstorms are expected on Tuesday
and Tuesday night from the Southern Plains to the Great Lakes.

...Synopsis...
The western US trough will eject across the Rockies on Tuesday with
strengthening westerly flow overspreading the Plains into the Great
Lakes Region. A surface low will deepen across western KS/NE with a
warm front lifting across the Lower Missouri Valley into the Great
Lakes and sharpening dryline across the southern/central Plains. A
cold front will sag southward across the Upper Midwest/Great Lakes
vicinity. The surface trough/dryline and the boundary across the
Great Lakes will become a focus for thunderstorm activity through
the forecast period.

...Lower MO Valley to the Great Lakes...
Convective coverage will overlap the start of the period near 12z on
Tuesday across portions of the Midwest/Great Lakes Region. Trends
are for relatively quick clearing across portions of central Iowa
into Illinois. As the warm front lifts northward, strong daytime
heating is expected amid dew points in the low to mid 60s. It is
likely the air mass will recover with potential for moderate to
strong instability by the afternoon. Stronger height falls are not
expected across the region, as the main upper trough
will be focused well to the southwest. However, warm advection atop
a southward-sagging surface boundary should support isolated to
scattered storm development by late afternoon/evening. The primary
risk will be for large to very large hail ( some 2.5"+ in diameter)
and damaging wind.

By late afternoon/evening, 700 mb flow will strengthen (around 50-60
kts) with a plume of steep low to mid-level lapse rate nosing into
central Iowa/northern Illinois from the southwest. The 850 mb
low-level jet also increases, with large clockwise curved hodographs
developing with the resulting increase in low-level shear. If
supercells can develop and maintain residency along or south of the
warm front, a corridor of greater tornado risk (a couple of which
may be strong tornadoes) may present itself.

Consideration was given to a 30 percent area (primarily hail
driven). With some uncertainty remaining in morning convection and
coverage of storms in the afternoon/evening, the 15% was maintained
with this outlook until more information can be gleaned from hi-res
guidance.

...Southern Plains...
Ahead of the dryline across the Southern Plains, strong daytime
heating is expected. Large-scale ascent will begin overspreading the
region by late afternoon/evening as the western upper trough finally
begins to eject eastward. As this occurs, mixing and convergence
along a surface dryline should support storm development by around
00z. If little convective development occurs on D2/Monday, a
relatively undisturbed moist/very unstable air mass will be in
place. It is likely that rather robust thunderstorm development will
occur along the dryline, with the primary mode being supercelluar.
Large to very large hail (2 to locally 2.5+ inches in diameter),
damaging wind, and a couple of tornadoes will be possible. Given
that deep layer shear profiles have more of a parallel component to
the dryline, storm interactions may keep the period of more discrete
supercell thunderstorms short, with a shift to clusters of mix-mode
supercell and multi-cell storms.

..Thornton.. 04/12/2026

$$