The National Weather Service in Great Falls issued a Flash Flood Watch on Thursday, September 18th at 3:21 AM MDT, with the watch extending through midnight Saturday, September 20th — a roughly 45-hour window covering a large swath of central and southwest Montana. The Helena area is included in the watch zone.
The NWS specifically called out the Horse Gulch area and burn scars left by wildfires during the summer of 2026 as zones of heightened concern. Burn scars dramatically accelerate runoff because the ground cover and root systems that would normally slow water absorption have been destroyed. Debris flows — fast-moving slurries of mud, ash, and loose material — are a documented hazard on burned slopes even in rainfall events that would be unremarkable on unburned terrain.
The watch area spans Big Belt, Bridger, and Castle Mountains, along with the Elkhorn and Boulder Mountains and the Little Belt and Highwood Mountains in central Montana, extending into the Gallatin Valley in southwest Montana. That broad geographic footprint reflects how widespread the recent fire activity was across the region this summer.
Residents living near drainages below burned hillsides should take the watch seriously. The NWS recommends having a plan for rapid evacuation if conditions deteriorate, and avoiding any travel through flooded roadways or drainages during and after heavy rainfall. Updates and any watch upgrades to warnings would come through the NWS Great Falls office.