The National Weather Service office in Great Falls issued a Flood Watch for the Helena Valley and Canyon Ferry area Friday morning, September 19th, with the watch running from 3:09 AM MDT through 6:00 PM MDT the same day. The watch covered portions of central and southwest Montana, including Meagher County valleys and the Gallatin Valley.
The NWS cited excessive rainfall as the driver, with the watch indicating that flooding remained possible — not certain — through Friday afternoon. Residents in low-lying and flood-prone locations were flagged as most at risk from excessive runoff. The Canyon Ferry area, which drains a substantial watershed above Helena, can move water quickly into the valley when saturated soils lose their capacity to absorb additional rainfall.
This watch was issued separately from, but overlapping with, a Flash Flood Watch that had been posted the previous day covering burn scar areas in the region. Residents near drainage channels, gulches, or other low-lying terrain were advised to stay alert to changing conditions and to avoid attempting to cross flooded roadways.