Debris Flow in Sanders County, Montana

A training thunderstorm positioned over the Eddy basin dropped between 1.41 and 1.60 inches of rain in less than 1.5 hours. This high-intensity rainfall fell on steep terrain, rapidly saturating soils and triggering multiple mudslides on the mountainside north of Highway 200. The resulting debris flow rushed down the slope 2 miles east-southeast of Eddy, uprooting at least one large tree and dislodging a boulder the size of a small car. The massive boulder and associated mud slide debris slid directly into the roadway, completely blocking traffic between mile markers 63 and 64. The local fire department and state road crews responded to manage traffic and clear the slide area.

Between May 28 and June 4, 2026, a very slow-moving upper-level low-pressure system over Montana tapped into moisture from the Gulf of America, bringing heavy and widespread precipitation to western Montana. Prior to this event, several locations had already received significant moisture in May, leaving soils saturated and mountain runoff elevated. The combination of intense rainfall and ongoing snowmelt led to swollen rivers, and overwhelmed small streams, and flooded local irrigation canals. Intense thunderstorms brought heavy rain-rates in Sanders County resulting in mudslides.