Flood — Sanders, Montana

2025-12-11 · near Thompson Falls, Sanders, Montana

Event narrative

At approximately 0400MST on December 11, a massive landslide occurred near Eagle View Lane, roughly 2 miles south-southwest of Bull Lake. The debris flow significantly damaged a residential garage, and the residents were unharmed. An Emergency Declaration was issued to address the lowland flooding and debris removal. Highway 56 near Bull Lake was forced to close between mileposts 16.7 and 17.2 after overwhelmed culverts allowed stream overflow to inundate the roadway. The emergency manager reported that over a dozen properties were isolated from Highway 56, either by a foot of water over access bridges or by an approximate 50-yard-wide flow of sediment-laden water separating residences from the main road.

A bridge on Montana Highway 471/Thompson Pass Road, near milepost 15, was washed out by Prospect Creek, resulting in a road closure. Prospect Creek also flooded the Prospect Creek campground at the Wild Coyote, located 7 miles up Prospect from Highway 200.

Wider weather episode

Record precipitation fell as a prolonged atmospheric river event gripped the region from December 6 through 12. Much like a garden hose being moved back and forth, the jet stream shifted the focus of this moisture plume across the Pacific Northwest, repeatedly drenching parts of northern Idaho and western Montana. Between December 10 and 11, 2025, the atmospheric river specifically focused on northwest Montana, and produced record rainfall and catastrophic rain-on-snow flooding. A saturated snowpack acted as a sponge until reaching capacity late December 10, when warm nighttime temperatures and rainfall rates of 0.30-0.50 inch per hour below 7,000 feet triggered rapid runoff. Total precipitation amounts ranged from 4 to 7 inches within the 24 hours leading up to the event.

Significant flooding and landslides occurred across Lincoln, western Sanders, and western Mineral Counties, where numerous tributaries and streams overwhelmed their banks. The event resulted in eight bridge washouts in Lincoln County, with one additional bridge lost in both Mineral and Sanders Counties. This was one of the most significant rain-on-snow December events since 1933, when 12 bridges were washed out in Lincoln County alone. On December 11, Governor Greg Gianforte issued Executive Order 9-2025 declaring a flooding disaster in northwestern Montana. Following a formal request on December 16, a Presidential Emergency Declaration was approved to provide federal aid for Lincoln and Sanders counties and the Blackfeet Nation. Preliminary assessments placed infrastructure and property damage at $35.1 million for all three counties. The only injury was from a man who drove off the Farm-to-Market Road bridge into the waters below. He was able to escape with only scrapes and bruises. This atmospheric river event also brought high winds to the mountains and a few valley locations. Precipitation levels reaching 238 percent of normal in British Columbia and the Glacier Region sent inflows into Flathead Lake soaring to over 300 percent of average. The West Central Montana Avalanche Center reported several wet loose avalanches and mudslides near steep highway cuts near Lolo Pass on December 11. They reported that the highway crew had to clear debris from the road. Rockfall was also reported along MT-1, north of Georgetown Lake.

View location on OpenStreetMap → (47.4888, -115.6302)

Source: NOAA Storm Events Database, event_id 1306058. Narrative written by the NWS forecast office that issued the report.