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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0754 AM CDT Mon Aug 29 2022

Valid 291300Z - 301200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM THE
MISSISSIPPI RIVER ALONG THE ILLINOIS/IOWA BORDER ACROSS NORTHERN
ILLINOIS TO NORTHWESTERN INDIANA AND SOUTHWESTERN LOWER MICHIGAN...

...SUMMARY...
Severe thunderstorm winds are expected today across parts of the
middle Mississippi Valley into the southern Lake Michigan region.

...Synopsis...
The mid/upper-level pattern this period will be characterized by an
expanding trough -- embedded in otherwise zonal flow -- and
initially located from a low over southeastern MB to northern NE. 
By 00Z, this trough will move eastward to northwestern ON, western
Lake Superior, western IA, and northwestern MO.  Meanwhile, it
should amplify as a shortwave perturbation digs through the back of
the associated cyclonic-flow field, across the Dakotas to IA.  By
12Z, the still-amplifying trough should extend from near James Bay 
down Lake Michigan to southern IL.

At the surface, 11Z analysis indicated a cold front from western
Lake Superior across western WI, central IA, to northeastern/north-
central KS and a low near HLC.  By 00Z, the front should reach
northern Lower MI, northern IL, northern MO, and central/
southwestern KS.  By 12Z, it should reach northwestern OH, the
Ozarks, and west-central/southwestern OK.

...Mid Mississippi Valley to southern Lake Michigan region...
At least sporadic severe wind gusts are expected through the day as
a co*plex of thunderstorms organizes this morning in Iowa, then
proceeds eastward through afternoon across northern IL and perhaps
extreme southern WI, toward the southern Lake Michigan vicinity
(including Chicago metro).  Whether or not the event technically
meets derecho criteria, a swath of strong-severe convective wind is
expected, centered in the greatest risk area.  Some gusts may reach
significant (65+ kt) speeds, capable of locally substantial damage.

This threat should develop beneath the southeastern fringe of the
height falls, large-scale lift/DCVA, and increasing flow aloft
preceding the mid/upper-level trough.  The most likely origin for
the severe convection appears to be an organizing band of initially
elevated, post-frontal thunderstorms, and associated low/middle-
level UVV plume over western/central IA.  This activity exhibits
cooling to steady trends in IR cloud tops and coverage/intensity of
high radar reflectivity, with variable lightning tendencies.  The
convection should cross the much-slower-moving cold front in the
next couple hours, reaching a minimally inhibited warm sector with
rich low-level moisture (surface dewpoints co*monly in the low 70s
F).  See SPC mesoscale discussion 1739 for near-term coverage.

Either an intensified version of this convection, or new development
on the leading edge of the associated UVV field, should grow rapidly
upscale and evolve into a damaging QLCS or bow echo.  The co*plex
may develop a self-sustaining vertical circulation with a rear-
inflow jet, as it crosses the Mississippi River and northern IL into
a diurnally destabilizing boundary layer, further reinforcing its
severe-wind potential.  With steep (7-8 deg C/km) midlevel lapse
rates, preconvective MLCAPE may reach 3000-4000 J/kg, based on the
modified 12Z DVN RAOB (already showing 3000 J/kg MLCAPE) and several
models' forecast soundings.  The MCS should backbuild southwestward
somewhat as it crosses northern IL, while also forward-propagating
toward southern Lower MI and northern IN.  Activity should outrun
the plume of favorable moisture/instability this evening over the
central IN/northwestern OH corridor, then weaken.  Farther southwest
across central/western IL and MO, weaker deep-layer flow/UVV support
should contribute to lesser convective coverage, but given the
available moisture/instability, sporadic severe hail/gusts are still
possible.

...KS/OK to southern High Plains...
Isolated to scattered thunderstorms -- in the form of discrete and
clustered multicells -- should develop by afternoon along/ahead of
the front, and near prefrontal outflow/differential-heating
boundaries.  Low/middle-level winds and shear will be weak, limiting
overall organization. However, rich low-level moisture will underlie
favorable deep-layer lapse rates, amid a deep troposphere.  This
will enable diurnal heating to boost MLCAPE into the 2000-3000 J/kg
range over much of KS and OK ahead of the front, and 1500-2500 J/kg
over the southern High Plains.  Locally severe downbursts and
isolated large hail will be the main concerns.  Some upscale
convective evolution to mesobeta-scale clusters may occur and
concentrate severe potential within the broader "marginal" area;
however, predictability for such processes under weak ambient
flow/forcing is too low to assign greater unconditional
probabilities at this time.

..Edwards/Goss.. 08/29/2022