Flood Warning in Effect for Western Montana as Snowmelt and Heavy Rain Drive Streams Higher
CHICO, Calif. — June 1, 2026
The National Weather Service office in Missoula extended a Flood Warning Monday evening for portions of Flathead, Lake, and Sanders counties in northwestern Montana, citing small-stream flooding driven by a combination of recent heavy rainfall and active snowmelt running off the Mission and Swan mountains.
The warning, originally issued earlier in the day, was reissued at 7:25 p.m. MDT and remains in effect until 7:30 a.m. MDT Tuesday. Communities in the warned area include Ronan, St. Ignatius, and Pablo in western Lake County.
“Small stream flooding caused by excessive rainfall continues,” NWS Missoula said in the formal warning text. “Flooding of rivers, creeks, streams, and other low-lying and flood-prone locations is imminent or occurring. Streams may continue to rise due to excess runoff from earlier rainfall.”
Between one inch of rainfall in the valleys and five inches in the mountains has fallen across the warned area since the system began, the agency said. An additional 0.2 to 0.5 inches is forecast through Tuesday morning.
What's driving the flooding
Western Montana has been under a multi-day wet pattern that began over the weekend. NWS Missoula issued a Hydrologic Outlook on May 29 forecasting widespread moderate to heavy precipitation across Flathead, Lake, Missoula, Powell, Granite, Ravalli, Deer Lodge, and Silver Bow counties from May 30 through June 1, with total precipitation amounts of one to three inches and locally higher amounts in the higher terrain along the Continental Divide.
The flooding risk is being amplified by ongoing snowmelt. Stream and river levels were already running above normal heading into the weekend, and the additional rainfall has accelerated runoff. NWS Missoula's hydrology page shows mainstem rivers in Lake County including the Swan River near Bigfork and the Flathead River near Polson among the gauges under active observation.
According to the hydrologic outlook, the Clark Fork River near Missoula was forecast to reach near 8 feet by Monday afternoon, and the Flathead River near Columbia Falls was projected to reach near 14 feet by Tuesday night, June 2.
NWS Missoula issues 'Plan, Prepare, Act' briefing
In a graphical briefing posted Monday, NWS Missoula said additional rainfall through Tuesday could total 0.5 to 1 inch in most areas, with up to 2 inches possible along the Continental Divide. The agency flagged risks for minor flooding in urban and flood-prone areas, rising small streams and rivers, and an elevated risk for mudslides, debris flows, and runoff issues in steep terrain.
The forecast office's recommended action items: locate flood-prone areas before traveling, clean gutters and storm drains, test sump pumps, and never drive through standing water on roadways.
Wider Northern Plains pattern
The Montana flooding is one piece of a broader unsettled pattern across the Northern Plains and Pacific Northwest as June begins. Forecasters with the Climate Prediction Center are calling for above-average rain chances through the 6th to 10th of the month across a large portion of the central and western United States.
In neighboring Alberta, Environment and Climate Change Canada has issued more than 300 weather alerts, with widespread 50 to 100 millimeters of rainfall provincewide and a Bow River Flood Watch in effect near Lake Louise. Gusts to 90 kilometers per hour and 30 to 50 centimeters of snow in higher peaks have accompanied the system as it tracks east toward Saskatchewan and Manitoba.
In Texas, the Weather Prediction Center has highlighted parts of West Texas, eastern New Mexico, the Trans-Pecos, the Big Bend, and the Texas Panhandle for localized scattered flash flooding Tuesday into Tuesday night and again Wednesday, with rainfall rates of two to three inches per hour possible in the strongest storms.
What to watch
The Lake County Flood Warning is scheduled to expire at 7:30 a.m. MDT Tuesday but could be extended or expanded if additional rainfall over the Mission and Swan ranges produces continued runoff. The NWS will reassess river levels during the morning hydrologic update.
Residents in flood-prone parts of northwestern Montana should monitor their local NWS Missoula forecast office and avoid travel through any flooded roadway. The standard NWS guidance: “Turn around, don't drown when encountering flooded roads. Most flood deaths occur in vehicles.”
About flood preparedness
Homeowners in areas under active flood warnings have limited time to deploy barriers. FEMA recommends pre-staging materials before any warning is issued, particularly for properties on small-stream floodplains where rises can occur in under an hour. StormBag, the FEMA- and DHS-approved rapid-deploy sandbag manufactured in Chico, Calif., activates with three minutes of fresh water and stacks to form a barrier comparable to a traditional sandbag without the labor of shoveling sand. The StormBag Flood Watch tool provides free real-time NWS flood alerts by ZIP code, including Lake County, Montana.
This is a developing story. Updates will follow as river forecasts are revised.
