Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0800 PM CDT Mon Jul 20 2026
Valid 210100Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE UPPER GREAT LAKES INTO THE LOWER MISSOURI VALLEY...
...SUMMARY...
Severe thunderstorms capable of producing damaging wind gusts,
severe hail, and a couple of tornadoes will continue across portions
of the Upper Great Lakes and Lower Missouri Valley through late
tonight.
...01Z Update...
Water-vapor imagery and VWP data indicate a robust midlevel wave and
accompanying belt of 50-60-kt west-northwesterly flow overspreading
the Upper Midwest, and this feature will continue east-southeastward
across the Great Lakes region tonight. In the low-levels, an
attendant cold front will continue east-southeastward across this
region as well. In the Upper Great Lakes and Midwest, 50-60 kt of
deep-layer shear (sampled by regional VWPs) oriented perpendicular
to the cold front and a relatively narrow corridor of strong
pre-frontal buoyancy (around 3000 J/kg MLCAPE) will continue to
promote semi-discrete supercell structures. Locally damaging wind
gusts, severe hail, and a couple of tornadoes will be possible with
this activity, given ample low-level hodograph curvature (around 250
m2/s2 effective SRH) beneath the core of a 40-kt LLJ. This activity
will generally spread east-southeastward across parts of Lower MI
tonight, where a continued risk of damaging wind gusts, severe hail,
and a tornado or two will continue ahead of the cold front before
encountering increasingly stable air.
Farther south, a couple organized clusters are tracking southward
across parts of southern IA and western IL. Given strong cold pools
with this activity, the primary concern will be severe wind gusts
and isolated/sporadic hail. These storms will continue tracking
south-southeastward along a surface-based buoyancy gradient before
gradually weakening overnight.
..Weinman.. 07/21/2026
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