809
ACUS48 KWNS 210720
SWOD48
SPC AC 210718

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0218 AM CDT Tue Jul 21 2026

Valid 241200Z - 291200Z

...DISCUSSION...
...Great Lakes/Midwest...

An amplified upper ridge will persist across the Plains and Rockies
through early next week. Periods of strengthening northwesterly
mid/upper flow are expected on the eastern periphery of the upper
ridge as a series of upper shortwave troughs move across the
Canadian Prairies and glance the Great Lakes vicinity, mainly Day
5-7/Sat-Mon. This could support areas of severe thunderstorm
potential across parts of the Upper Midwest to the Ohio Valley
vicinity during this time as stronger northwesterly flow overspreads
a seasonally moist and unstable airmass. However, both traditional
physics-based NWP and ML/AI NWP are inconsistent and/or show
relatively low/broad probability areas -- increasing uncertainty in
timing and spatial delineation of severe potential. Given the
proximity to the upper ridge, capping may be a concern. Trends will
be monitored and severe probabilities may become necessary is
confidence increases in subsequent outlooks.

..Leitman.. 07/21/2026