Mesoscale Discussion 1162
NWS Storm Prediction Center Norman OK
0106 PM CDT Tue Jul 06 2021
Areas affected...northeast Nebraska southeast South Dakota and
portions of Minnesota Iowa and Wisconsin
Concerning...Severe potential...Watch possible=20
Valid 061806Z - 062000Z
Probability of Watch Issuance...60 percent
SUMMARY...Strong/severe storms developing ahead of and along a
remnant MCV/stationary front through the upper Midwest may pose a
severe risk as they move northeast through the day. Severe hail and
damaging wind gusts appear to be the mean threats. Convective trends
are being monitored as a weather watch may be needed.
DISCUSSION...As observed by regional radar mosaics and midday
visible imagery, a cluster of elevated thunderstorms has shown signs
of organization/intensification this morning across portions of
Nebraska, and south Dakota. Likely driven by enhanced lift ahead of
the MCV and along the stationary front, these storms should
gradually become surface based as they track northeastward.
Downstream, clearing skies south of the front have allowed
temperatures to warm into the low to mid 80s F across southern
Minnesota and far northern Iowa. To the north, residual cloud cover
has limited heating so far, but breaks in the clouds should allow
some warming through the afternoon. With the warm temperatures and
dewpoints in the mid to upper 60s F, moderate buoyancy (1500-2000
J/kg MLCAPE) is forecast to materialize despite modest mid-level
lapse rates. As lift from the approaching MCV increases, additional thunderstorm development appears likely along and north of the
stationary front through southern Minnesota and farther southwest
along the surging cold front in central Nebraska. Regional 12z
soundings and VWPs show enhanced mid-level shear associated with the
MCV across portions of South Dakota and northeastern Nebraska. 30-35
kts of effective shear should support organized short line segments
and a few supercells this afternoon. Hail and damaging wind gusts
appear to be the most likely threat, though a brief tornado will be
possible with greater low-level shear from backed surface flow along
the boundary through southern Minnesota and western Wisconsin.
Upscale growth into a forward propagating MCS appears likely later
this evening as storms congeal heading into southwestern Wisconsin.
A somewhat more organized wind threat may evolve there if a deeper
cold pool can become established. Given the favorable environment
and potential storm coverage, convective trends are being monitored.
A weather watch may be needed over portions of the area later this afternoon/evening as convection becomes more organized.
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