The National Weather Service office in Great Falls issued a Dense Fog Advisory early Tuesday morning, warning drivers across a wide swath of central Montana — including the Gates of the Mountains corridor — to expect visibility as low as a quarter mile in freezing fog through noon.
The advisory, issued at 3:14 a.m., covered an unusually broad area: Cascade County below 5,000 feet, Eastern Glacier, Western Toole, Central and Eastern Pondera, Eastern Teton, Eastern Toole and Liberty, Fergus County below 4,500 feet, Judith Basin County, Judith Gap, and both the Northern and Southern High Plains. The Gates of the Mountains, which funnels commuter and recreational traffic along U.S. 15 north of Helena, was specifically called out in the advisory.
Freezing fog differs from ordinary fog in that moisture deposits as ice on road surfaces, guardrails, and bridges — conditions that can catch drivers off guard even at low speeds. The NWS advised motorists to slow down, use low-beam headlights, and allow extra following distance. The advisory expired at noon MDT.
Helena sits at the southern edge of the affected zone, but drivers heading north toward Great Falls or east toward Townsend faced the worst of the conditions during the morning commute. Residents with travel planned along the Gates of the Mountains stretch of I-15 were advised to check road conditions before departing.