Mesoscale Discussion 1877
NWS Storm Prediction Center Norman OK
0920 AM CDT Sun Aug 09 2026

Areas affected...Portions of southern Wisconsin into far northern
Illinois

Concerning...Severe potential...Watch possible 

Valid 091420Z - 091545Z

Probability of Watch Issuance...40 percent

SUMMARY...An organized bowing structure, likely elevated at present
time, could become near surface based as it moves into southeastern
Wisconsin and adjacent northern Illinois. Wind damage would be the
main threat. A watch is possible should observational trends
warrant.

DISCUSSION...A small bowing cluster has been moving southeastward
this morning. This activity has remained elevated thus far, but the
airmass ahead of it is slowly destabilizing. Dewpoints in northern
Illinois/southern Wisconsin have increased over the past couple of
hours. The main limiter in terms of destabilization has been the
cloud cover/smoke that has reduced insolation. Based on forecast
soundings, if temperatures can reach the mid 70s F the storms will
be at least near surface based. Given the current organization of
ongoing convection, there may be an increase in damaging wind
potential over the next couple of hours. The need for a watch is
uncertain and will depend on observation trends.

..Wendt/Hart.. 08/09/2026

...Please see www.spc.noaa.gov for graphic product...

ATTN...WFO...LOT...MKX...ARX...

LAT...LON   42338865 42578899 43008959 43609043 43968955 43808901
            43158779 42748767 42538767 42418772 42278830 42338865 

MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0737 AM CDT Sun Aug 09 2026

Valid 091300Z - 101200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE MIDWEST...

...SUMMARY...
Scattered damaging winds may occur today into this evening from
southern Minnesota and eastern Iowa eastward across parts of
northern Illinois, southern Wisconsin, southern Lower Michigan,
northwest Ohio, and northern Indiana.  Damaging wind and hail are
also expected across portions of the Dakotas.

...Midwest...
Radar/satellite composite shows a corridor of showers/thunderstorms
from northern MO into southern MN and western WI associated with
isentropic lift on the nose of a 40-kt southwesterly LLJ.  A
localized risk for hail/wind may accompany this activity this
morning as it shifts eastward across the MS River towards Lake MI
through midday.  Considerable uncertainty remains regarding the
severe forecast for the eastern IA into the southern Great Lakes
portion of the Slight Risk.  Showers/thunderstorms and related
convective debris/outflow will be influential on airmass recovery
later this afternoon.  It seems plausible a warm front draped over
the Corn Belt this morning will slowly advance northward into the
southwest Great Lakes with an increasingly unstable airmass
developing to the south/west of this convectively augmented
baroclinic zone.  

Model forecast soundings show ample CAPE aided by the northern rim
of lower to mid 70s F surface dewpoints into northern portions of
IL/IN.  Adequately strong and vertically veering wind profiles will
support 30-40 kt effective shear magnitudes.  Low-level SRH may also
be locally boosted in the vicinity of the warm front/effective
boundary, which could then play a role in severe potential if a
supercell or linear segments were to develop and favorably interact
within this corridor.  Rather poor depiction of this morning's
thunderstorm evolution (i.e., 00z HREF members) casts large
uncertainty where a couple of more intense thunderstorm clusters
will ultimately develop.  It seems the greatest potential for severe
will be centered over northern IL later this afternoon through the
evening, but confidence remains low regarding details and the need
for spatial refinements of the severe risk area and the need for
potential higher probabilities.

...Dakotas and western NE...
A surface front is expected to push southward across the central
Plains, becoming oriented across northern KS by tonight.  Low-level
warm advection atop the boundary, and surface winds becoming
south/southeasterly with time will maintain 60s dewpoints across the
region.  Within this post-frontal upslope regime, a reservoir of
mainly 60s F dewpoints will reside beneath moderate northwesterly
flow aloft.  Supercell wind profiles and steep low-level lapse rates
will support initial storms capable of large hail and severe gusts,
especially as this activity over the western Dakotas moves
southeastward into richer moisture.  A small cluster may eventually
evolve during the overnight with an attendant risk for severe gusts
and perhaps large hail.

...Southern Appalachians...
Scattered thunderstorm development is expected over higher terrain
within a seasonally moist and unstable airmass.  Steepening
low-level lapse rates and high PW values may support locally strong
gusts with wet microbursts through early evening.

...AZ...
Modest easterly mid/upper flow will persist across the region on the
southern periphery of an upper high over the Four Corners.  Another
day of hot conditions will promote steep lapse rates and modest
destabilization.  As convection develops over higher terrain and
spread westward, strong outflow gusts may occur.

..Smith/Kerr.. 08/09/2026