971 

ACUS02 KWNS 131731
SWODY2
SPC AC 131729

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1229 PM CDT Mon Apr 13 2026

Valid 141200Z - 151200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF IOWA INTO NORTHERN ILLINOIS AND SOUTHERN WISCONSIN...

...SUMMARY...
Severe thunderstorms are expected on Tuesday and Tuesday night from
the Southern Plains to the Great Lakes. Large to very large hail, a
few tornadoes (some strong), and damaging wind gusts will be
possible, particularly across parts of eastern Iowa, northern
Illinois, and southern Wisconsin. Additional strong storms, mainly
producing strong wind gusts, will be possible across parts of the
Northeast.

...Synopsis...
The western US trough will eject across the Four Corners region into
the Intermountain West, with strong southwesterly flow overspreading
the Rockies into the central/southern Plains and Upper Midwest. A
shortwave trough will pivot through this flow across the Upper
Midwest through the period. A surface low will be centered over the
Mid-MO Valley for much of the period, with a warm front extending
east/northeast from north-central IA into southern WI and central
Lower MI. Meanwhile, a dryline will extend southwest across eastern
KS into western TX. These features will be the focus of scattered
thunderstorm development through the afternoon and evening.

...Mid-Missouri Valley and Great Lakes Region...
Strong daytime heating is expected along and south of the warm from
north-central IA into southern WI and lower MI Tuesday afternoon.
This in combination with dew points in the low to mid 60s will yield
moderate to strong instability (with MLCAPE around 1500-2500 J/kg).
Scattered thunderstorms are likely to develop around 20z. Given deep
layer shear around 40 kts, storm mode will be supercellular.
Initially, low-level shear will be marginal, with generally straight
and elongated hodographs. In addition, northeasterly storm motions
will favor crossing the warm front to the cool side of the boundary.
This will make the primary threat large to very large hail (some
2-3+ inches in diameter). With time, and as the low-level jet
increases during the evening, convection may consolidate/grow
upscale into one or more bowing segments and progress eastward into
Lower MI/IN/OH, posing a continued risk for hail and an increasing
risk for damaging wind gusts.

As the strengthening 850-700 mb low-level jet axis will nudge into
central IA/northern MO/northern IL, it will usher in a plume of
steep low to mid-level lapse rates and enlarge low-level hodographs,
increasing tornado potential. While there remains some uncertainty,
there is signal within hi-res guidance from the HREF for sustained
UH tracks south of the warm front. CAM guidance varies on how the
scenario will play out. As mentioned above, a few CAM solutions
favor clustering/linear development by the evening. Should a more
discrete supercell or two be able to root along or south of the
boundary, a few tornadoes will be possible (some strong EF2+).
Nonetheless, even with a more linear mode increasing low-level shear
will favor and increasing chance for line embedded tornadoes.

...Southern Plains into eastern Kansas/western Missouri...
Thunderstorm development is likely along the dryline across the
southern Plains Tuesday afternoon. Strong capping with remain
through most of the morning, but strong heating and convergence
along the dryline favor at least isolated thunderstorm development
by around 19-20z. The environment ahead of the dryline will be
characterized by moderate to strong instability, steep lapse rates,
and favorable deep layer shear profiles to support supercells. Large
to very large hail (1-2+ inches in diameter), damaging winds, and
perhaps a tornado.

...Northeast...
Rounds of thunderstorms are expected during the afternoon and
evening within a warm advection regime. MLCAPE should increase to
around 1000 J/kg within a moistening low-level air mass. Strong
deep-layer westerly flow and steepening low-level lapse rates will
support isolated strong wind gusts across the region.

..Thornton.. 04/13/2026

$$