Debris Flow and Flooding in Montana, May 28 to 31, 2026

Widespread high water affected the Flathead River basin. Anticipating heavy rainfall, operators at the Hungry Horse Dam opened the spillway gates at 1137MST on May 28 to manage reservoir capacity, causing significant downstream rises. On Friday morning, May 28, the City of Columbia Falls temporarily closed the back portion of River's Edge Park to the public due to early inundation. The Flathead River at Columbia Falls (CFMM8) crested at 13.78 feet with a discharge of 46,400 CFS on the evening of May 29, remaining above the minor flood stage of 13.0 feet. A subsequent NWS flood survey on June 1 at 1025MST documented high water completely surrounding private residential properties near the confluence of the South Fork and Middle Fork of the Flathead River. Floodwaters fully encircled a home 1 mile west of Hungry Horse, though the water had not yet breached the structural foundation or entered the living spaces at the time of the inspection.

Widespread small stream, agricultural, and infrastructural flooding occurred across the Mission Valley due to accelerated snowmelt and 4 to 6 inches of rainfall over a four-day period. A private weather station located 3 miles east-northeast of Pablo measured a total of 5.09 inches of rain from Friday through Monday, while another station just north of the Mission Reservoir measured 3.46 inches. Initial minor flooding began on Friday evening, May 29, when a storm dropped 0.50 to 0.60 inches of rain along the eastern side of the valley, flooding one-third of a private property near St. Ignatius. Runoff rapidly filled local irrigation systems, causing widespread issues. |At 0600MST on May 31, the lower cylinder flood gate at Mission Dam failed during a high-flow period. While flows were already elevated, this mechanical failure induced a dynamic flow condition where discharges dropped momentarily until emergency teams opened the upper cylinder gate to stabilize the dam, returning outflow into Mission Creek to approximately 350 CFS. At 1000MST, Agency Creek breached its banks, flooding low-lying pastures between Jocko and Agency Roads. At 1300MST, North Crow Creek overflowed, inundating properties along Minesinger Trail. |At 1430MST, the Pablo Feeder Canal experienced a structural failure at Skyline Drive and Caffrey Road, flooding adjacent crop fields. A multi-agency emergency response deployed heavy equipment and placed over 500 sandbags to reinforce the canal's south wall and repair the road base. |On June 1, NWS storm surveys documented extensive field flooding along Red Horn, Hillside, and Foothills Roads due to out-of-bank tributaries. North Crow Creek completely left its banks around Timberlane Road, inundating driveways and spreading water within 1 to 2 feet of a home's foundation. Floodwaters along the Pablo Feeder Canal completely submerged a length of Minesinger Trail and Mountain View Road, rendering them impassable to traffic. At 1400MST on June 1, with the Kicking Horse Reservoir at full capacity, all active water diversions from South Crow into the reservoir ceased. This forced the unbuffered, full natural flow from the South Crow drainage directly downstream into Crow Creek. The resulting surge caused Crow Creek to leave its banks entirely, backing up directly into a commercial greenhouse business (Bev's Bloomers). The floodwaters came within one foot of an adjacent home's foundation, and left a 6-foot property fence completely underwater. Severe road washouts were also reported north of Arlee on Saddle Mountain Road, where heavy rains stripped away soil and gravel to expose bedrock. Debris, mud, and water gushed across Highway MT-35 at milepost 10 on Monday evening, carrying a boulder the size of a small car onto the driving lanes near Woods Bay.

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.