Flandreau, SD Hail Storm – September 2025

What Happened

A severe hail storm crossed Flandreau, SD, on September 21, 2025, with the largest verified stones reaching 1.75 inches. The storm produced 12 NWS alert updates from late afternoon into the evening, with hail signals building from 1 inch to 1.75 inches as the cell matured.

The first alert came at 4:40 PM CDT with 1-inch hail from dual-polarization radar confidence. By 5:25 PM CDT, radar and spotter verification supported a 1-inch hail call. The storm strengthened through early evening. Alerts at 6:12 PM CDT and 6:31 PM CDT both carried 1.25-inch hail. At 6:48 PM CDT, the hail size increased to 1.5 inches.

The strongest radar-supported periods arrived after 7 PM CDT. Alerts at 7:23 PM CDT, 7:53 PM CDT, and 8:55 PM CDT all carried 1.75-inch hail, with intermediate alerts still holding 1.25-inch to 1.5-inch stones. The final alert at 9:51 PM CDT backed down to 1.25 inches as the storm weakened.

Field reports tracked the same sequence. A storm chaser reported increasing hail activity and a rotating wall cloud at 6:51 PM CDT. Around 7:00 PM CDT, spotters relayed 1-inch hail. At 7:35 PM CDT, a report described ping pong ball to golf ball size hail. Later reports placed quarter to half dollar hail near 8:30 PM CDT and quarters around 7:55 PM CDT. A broadcast-media relay at 9:15 PM CDT also noted 2-inch hail.

Damage Assessment

The ground reports point to repeated hail impacts across Flandreau during the evening storm cycle. Spotters described quarter-size hail, quarter to half dollar hail, and golf ball size hail in separate reports. The mix of sizes suggests multiple pulses of hail as the storm cycled through the area.

The reports did not focus on a single isolated strike point. They came in over several hours and included both public and spotter observations, along with radar-timed estimates. That pattern fits a broad hail swath with multiple bursts of larger stones rather than one brief pass.

The 2-inch report relayed by broadcast media came in at 9:15 PM CDT. It appears after the strongest radar period and after several earlier spotter reports of smaller hail. The sequence leaves a clear record of hail growth, peak intensity, and later tapering.

For surface damage, the most likely callouts are vehicle impacts, soft-metal dents, and exposed property hits in the areas reached by the later evening hail bursts. The report set does not identify one uniform damage path. It does show repeated hail contact in and around Flandreau as the storm strengthened, held severe size through the evening, and then eased.

What Contractors Should Know

This event built in stages. Crews working Flandreau should treat the late afternoon and evening window as the main inspection period, with the strongest hail reports clustered from 6:48 PM CDT through 9:15 PM CDT. Earlier reports at 4:40 PM CDT and 5:25 PM CDT were smaller, but the storm escalated after that.