The National Weather Service office in Great Falls issued a Dense Fog Advisory for the Helena area beginning early Monday, October 26, running through noon MDT. Visibility was reduced to one quarter mile or less in affected zones during the advisory period.
The advisory covered a wide swath of central Montana including the Canyon Ferry area, the Elkhorn and Boulder Mountains, the Missouri Headwaters corridor, the Madison River Valley, Gallatin Valley, Centennial Mountains, and portions of Beaverhead and Madison counties below 6,000 feet elevation. Drivers on routes in and out of Helena — including Highway 12 east toward Canyon Ferry and Interstate 15 north and south — faced the most significant visibility hazards during the morning commute window.
The NWS Great Falls office noted that low visibility conditions could make driving dangerous and recommended that motorists slow down, use low-beam headlights, and increase following distance. The advisory was set to expire at noon, with conditions expected to improve as the day warmed.