DES MOINES, IOWA — Severe weather is possible Sunday, August 9 from the Plains to the Great Lakes, with South Dakota, Nebraska and Iowa carrying the greatest severe weather potential within a broader Marginal Risk, Level 1 out of 5, according to an outlook updated at 3:26 AM ET Friday, August 7. As a cold front moves into South Dakota and Wisconsin, it will interact with a warm, humid air mass, triggering isolated thunderstorms across the region.
South Dakota, Nebraska, and Iowa Carry Greatest Hail Potential
The darker green corridor, marking the highest concentration of Sunday’s threat, stretches from near South Dakota southeast through Iowa and into northern Illinois, close to Chicago. Within this zone, forecasters specifically highlight South Dakota, Nebraska and Iowa as facing the greatest potential for large hail, distinguishing this area from the rest of the broader risk zone.
Sioux Falls sits directly within this highest-potential corridor, along with Des Moines, both positioned where the combination of the cold front and available moisture is expected to be most favorable for organized severe storm development.
Damaging Winds Remain the Primary Threat Across the Entire Zone
While large hail is specifically flagged for South Dakota, Nebraska and Iowa, forecasters note that damaging winds will be the primary threat across the entire Marginal Risk area, which extends much farther than the hail-specific zone. This broader Marginal Risk footprint stretches from the Pacific Northwest through the Rockies, Plains and into the Great Lakes, reaching as far east as Chicago and Detroit.
This means communities across a much wider swath, including Chicago, St. Louis and areas throughout the Plains, should watch for the potential of damaging wind gusts even if they fall outside the more concentrated hail threat zone centered on South Dakota, Nebraska and Iowa.
Timing for Sunday, August 9
The outlook is valid for Sunday, August 9, with the cold front expected to trigger isolated thunderstorms as it interacts with the warm, humid air mass in place across South Dakota and Wisconsin. A separate general thunderstorm designation also covers portions of the Southwest, including areas near Phoenix and Los Angeles, along with a stretch of Texas near Dallas…