Sioux Falls, S.D. – Drivers, outdoor workers, and event organizers in southeastern South Dakota should prepare for oppressive heat Saturday, with the National Weather Service warning of heat indices topping 105° and potentially reaching 110°. Conditions will peak during the afternoon, especially west of the James River Valley, where the combination of humidity and heat will strain anyone outdoors.
According to the National Weather Service in Sioux Falls, the heat expands east Friday into Saturday before easing slightly Sunday. Afternoon heat index readings will range from 95° to 103° Friday, climbing into dangerous triple digits Saturday. Motorists traveling I-29 or U.S. Highway 81 should use extra caution—heat can quickly impact vehicle performance, and sudden storms could reduce visibility.
Low chances for thunderstorms arrive Saturday night and continue through Sunday, with storm intensity and location still uncertain. Sunday night carries a slightly higher storm chance of 40%, which could bring gusty winds and heavy rain to localized areas.
Those outdoors should hydrate often, take frequent breaks in shade or air conditioning, and check on vulnerable neighbors. Limit strenuous activity during the hottest hours between 1 p.m. and 6 p.m.
The heat index should drop into the 90s by Sunday, but humidity will linger into early next week. No spotter activation is expected at this time, but updates may be issued if storm chances rise.
Five Day Forecast for Sioux Falls, S.D.
Saturday, Aug. 16: Mostly sunny, high near 91°. Southeast wind 5–10 mph.
Saturday Night: 30% chance of showers and thunderstorms. Low near 72°.
Sunday: 20% chance of storms. High near 89°.
Monday: Mostly sunny. High near 89°.
Tuesday: Mostly sunny. High near 87°.
