ACUS02 KWNS 161732
SPC AC 161730

Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1230 PM CDT Wed Jun 16 2021

Valid 171200Z - 181200Z


Widely scattered strong to severe thunderstorms are possible mainly
from Iowa into southern Wisconsin and northern Illinois Thursday and
Thursday night.  Large hail and damaging winds are possible with the
stronger storms.

A mid-level speed max over south-central Canada/North Dakota will
gradually move southeastward into the Upper Midwest/western Great
Lakes.  A surface trough/front will extend roughly from southern MN
into eastern NE during the mid afternoon and a warm front will
advance east-northeastward across parts of the western Great Lakes.
West to southwest low-level winds will maintain warm advection into
the region, and will likely support bouts of severe storms beginning
late afternoon across IA or southern MN, and eventually into IL

...Upper MS Valley/Great Lakes...
Models are indicating the possibility for a few showers or storms to
be ongoing Thursday morning anywhere from southern MN/western WI
southward into northeast MO via theta-e advection.  This early day
activity will likely diminish by late morning with destabilization
focusing near the surface trough.  The strongest buoyancy is
forecast across from eastern NE into IA, where heating and 65-70 deg
F dewpoints will contribute to MLCAPE ranging from 4000+ J/kg near
the MO River to 2500 J/kg in western WI.  As convective inhibition
weakens considerably by mid-late afternoon, isolated thunderstorms
are forecast.  Deep-layer shear will favor organized storms,
including supercell potential during the afternoon-early evening. 
As large-scale ascent increases during the evening, upscale growth
into a cluster will probably occur.  There is uncertainty how far
east/southeast the severe risk will develop Thursday night.  Have
left the convective outlook unchanged but additional adjustments to
the severe probabilities will probably be needed.

The southwest portion of the surface boundary will become draped
from west to east across NE on Thursday night.  Strengthening
warm-air advection coincident with a central Great Plains LLJ, may
lead to isolated storms developing north of the surface boundary. 
It is unclear at this time whether this activity would pose an
isolated risk for hail/wind---will defer this area to possibly being
included in later outlook updates.

..Smith.. 06/16/2021