Winter Weather in Lower Clark Fork Region, Montana

Light wintry precipitation, including probable freezing rain, led to slick travel along Interstate 90 west of Alberton and near St. Regis. Additionally, a hazardous layer of black ice formed on the Highway 200 bypass between Thompson Falls and Plains, causing vehicles to slide and lose traction at highway speeds.

A weak atmospheric river pushed into the Northern Rockies while a dry and very cold air mass was firmly entrenched across western Montana and north-central Idaho. This pre-existing cold pool proved highly resilient, and high temperatures largely remained at or below freezing in the valleys. As the warmer atmospheric river moisture eventually overran the sub-freezing surface layer, the snow transitioned into a dangerous period of freezing rain across several valleys. Because heavy cloud cover during the day prevented the sun from sufficiently heating the pavement, road surface temperatures remained stubbornly below freezing. This resulted in rapid black ice formation that caused severe travel disruptions, accidents, interstate highway closure, and at least one fatality.