Flash Flood in Roberts County, South Dakota

Roberts County Emergency Management reports that barricades were required at several locations where water has come up over highways and secondary roads, from portions of highway 15 near Wilmot all the way up to 123rd St 3 miles north of Agency Village.

A line of storms produced large hail and high winds during the afternoon and evening of August 5th, and into the early morning hours of August 6th. The largest sized hail measured at 3 inches in diameter was observed in Hoven. Later in the evening, a peak wind gust of 99 mph was recorded on a weather station out at Sandy Shore State Park, while the Watertown Regional Airport ASOS would record a peak gust of 68 mph. Over 40 trees were topped or downed as a result of these winds around the Lake Kampeska area. Additional sporadic tree and crop damage was noted elsewhere across northeast South Dakota.

Heavy rainfall would also lead to flooding with reports of several roads overtopped by water in the city of Watertown, the towns of Britton, Agency Village, and Wilmot, as well as portions of rural Codington, Roberts, and Marshall counties. Already saturated soils from a wet spring and summer were unable to absorb the 2 to 4 inches of rainfall, with the COOP observer in Wilmot measuring 3.63 inches and 3.31 inches of rainfall from a CoCoRaHS observer 1 mile south southeast of Kidder. These heavy rains would result in river flooding, mainly across the Big Sioux and its tributaries.