Severe thunderstorms should affect much of Minnesota into western
Wisconsin late this afternoon into early tonight, with large to very
large hail, damaging gusts, and a couple of tornadoes possible.
Damaging winds may also occur this afternoon from northern Illinois
into southeastern Wisconsin.

…MN and vicinity this afternoon into early tonight…
A well-defined midlevel trough will move eastward from western ND as
of mid-morning to northwestern MN tonight, and will be preceded by a
weakening MCV moving from eastern ND to northwestern MN today. The
primary associated surface cyclone will progress eastward across
SK/MB, as a trailing cold front/trough, likewise moves eastward
across the Dakotas to the MN border by this evening. Ahead of the
front/trough, a plume of steep midlevel lapse rates of 8-9 C/km
sampled in 12z soundings will act to cap a gradually moistening
boundary layer (mid-upper 60s dewpoints northern MN to low 70s
across southern MN by afternoon), and will allow MLCAPE to increase
to near 3000 J/kg. Stratus under the cap and lingering convection
in southeastern ND will tend to slow surface heating, but ascent
along the boundary will support weakening of convective inhibition
and thunderstorm development 21-23z across west central and
northwest MN. Storms will then spread eastward through late evening
and develop southward toward central MN, with greater uncertainty
regarding storm coverage with southward extent into IA/eastern NE
this evening.

Mixed convective modes are expected along and ahead of the surface
front/trough, with a few semi-discrete cells initially, and some
upscale growth into clusters/line segments expected by this evening.
Vertical shear will become sufficient for supercells as hodographs
lengthen and clockwise curvature increases some in the low levels,
as reflected by effective bulk shear of 35-45 kt and effective SRH
of 100-200 m2/s2. The steep midlevel lapse rates/large CAPE and
sufficiently long hodographs will favor isolated very large hail
(2-2.5 inch diameter) with the more discrete supercells initially,
and the threat will transition more to damaging winds of 60-70 mph
with upscale growth of convection. A couple of tornadoes will also
be possible with the initial supercells, and with embedded
circulations in line segments.

…Northern IL/southeastern WI this afternoon/evening…
An MCV will continue to move northeastward from southeastern IA
toward southeastern WI through this evening. Midlevel lapse rates
are poor, but surface heating in cloud breaks ahead of the MCV will
contribute to moderate buoyancy (MLCAPE of 1500-2000 J/kg), and
thunderstorm development will be possible by early-mid afternoon
near the MS River. A mix of clusters and embedded rotating storms
will be possible given modest enhancement of low-level shear ahead
of the MCV (effective SRH in excess of 100 m2/s2), with the