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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Sun Aug 28 2022

Valid 281300Z - 291200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER MUCH OF
MINNESOTA INTO WESTERN WISCONSIN...

...SUMMARY...
Severe thunderstorms should affect much of Minnesota into western
Wisconsin this afternoon and evening, with large to very large hail,
damaging gusts, and a few tornadoes possible.

...Synopsis...
The dominant mid/upper-level feature for this forecast period will
be a prominent northern-stream shortwave trough -- evident in
moisture-channel imagery from southern SK across east-central MT to
northern WY, with embedded low/vorticity max just north of the
international border.  By 00Z, the trough should move eastward to
southern MB, eastern ND and central SD.  By 12Z, it should reach
from near the ON/MB border across west-central MN to eastern SD and
northeastern NE.

Farther south, a weak shortwave trough was apparent from
southeastern MN south-southwestward across eastern KS and north-
central OK.  Satellite and co*posited radar-reflectivity animations
indicated an embedded MCV over northwestern MO.  For tracking
purposes, this feature appears to be fairly well-captured by the
latest deterministic RAP and GFS runs, and somewhat in the 00Z
ECMWF/06Z NAM.  The MCV and trailing vorticity lobe should move
northeastward across western/northern IL this afternoon, reaching
southeastern WI to central IL by around 00Z.  The MCV/trough will
move northeastward across Lower MI and Lake Huron overnight.

The 11Z surface analysis showed a cold front arching from eastern SK
across southwestern MB, to a low between PIR-MBG, then southwestward
over the NE Panhandle.  A warm front was drawn over northwestern ON,
eastern MN, northeastern IA, northwestern to east-central IL, and
eastern KY.  The low should weaken as the cold front shifts eastward
today.  By 00Z, the cold front should reach northeastern ND, west-
central/southwestern MN, northwestern IA, east-central/south-central
NE, and northeastern CO.  The warm front will move slowly eastward/
northeastward over the upper Mississippi Valley, Lake Superior and
Lake Michigan through the period.

...Upper Mississippi Valley region...
Scattered thunderstorms are forecast to develop by mid/late
afternoon from the international-border region (Northwest Angle and
Boundary Waters) southward across much of MN, and more conditionally
into parts of IA or eastern NE.  The most favorable parameter space
for supercells will be over MN, and these may produce significant/2+
inch hail relatively early in the overall convective cycle. 
Sporadic damaging to severe gusts are expected, along with the
threat of tornadoes from any sustained supercells or line-embedded
mesocirculations.

Height falls and DCVA/ascent aloft will spread across the outlook
area ahead of the progressive trough, from west-east, and near the
surface cold front.  Frontal lift and prefrontal warming of the
boundary layer should remove enough MLCINH to support convective
initiation, amidst surface dewpoints co*monly in the 60s to near 70
F.  In tandem with steep midlevel lapse rates related to the
northeastern rim of an EML, this should support peak/preconvective
MLCAPE in the 2500-3500 j/kg range between the cold and warm fronts.
A substantial portion of the CAPE will be in mid/upper levels, with
ample opportunity for intense and high-moisture-content updrafts in
hail-growth zones.  Strengthening flow aloft with the approach of
the trough will support supercell-favoring deep shear (effective-
shear magnitudes of 40-50 kt possible), as will veering of winds
with height in low levels.  Upscale aggregation of convection into
at least loosely organized clusters or lines may occur with time
into this evening, offering mainly damaging gusts, but with isolated
hail and some tornado threat.  Trailing multicell convection -- in
an environment of weaker shear but still-favorable buoyancy over the
IA/eastern NE region -- may support isolated severe gusts/hail.

...Northern IL to southern Lower MI...
Scattered thunderstorms, in a corridor of mesoscale UVV enhancement
preceding the MCV, will offer a marginal severe/damaging wind threat
this afternoon into early evening.  A plume of clouds/precip -- with
decreasing associated convective coverage, but still a few embedded
thunderstorms -- was noted near the MCV/vorticity lobe from southern
IA across western MO and southeastern KS.  Ahead of this activity,
and near and southwest of the weakening warm front, the boundary
layer will destabilize from both direct/diabatic surface heating and
low-level warm advection.  Though low-level flow and convergence
will be modest, lift should be relatively maximized at the outflow/
differential-heating zone near the leading edge of the advancing
cloud/precip plume.  As that impinges on a warm sector characterized
by mid 60s to near 70 F surface dewpoints and negligible CINH,
thunderstorms should develop or re-intensify.  With limited vertical
shear (curved but small hodographs and effective-shear magnitudes
around 25-35 kt), multicells in clusters and line segments should be
the main mode.  Convection should weaken into central/southeastern
Lower MI this evening as it encounters a more-stable boundary layer.

...OK...
Widely scattered to scattered thunderstorms are expected to offer a
threat for isolated/localized severe gusts -- mainly mid/late
afternoon into early evening.  With early-morning clouds debris
dissipating and moving away, strong surface heating is expected
through the day, with weak lift focused along residual boundary(s)
and beneath the southern fringe of the mid/upper trough.  Deeper/
stronger boundary-layer mixing should occur over western parts where
PW and surface dewpoints are lower.  Associated MLCAPE and DCAPE
values around 1500 J/kg, amidst weak deep shear, will support
downdraft acceleration through the subcloud layer.  Farther east,
more heavily water-loaded downbursts are possible with MLCAPE
2000-3000 J/kg in the inflow layer.  The gust threat should wane
this evening with increasing coverage of outflow air, and greater
stability in the remaining boundary layer.

..Edwards/Goss.. 08/28/2022