The National Weather Service issued a Special Weather Statement early Wednesday morning warning of patchy dense fog across the Helena Valley, with visibility dropping below a half mile in some areas as of the 5:15 a.m. advisory.
The NWS cautioned drivers to be alert for quickly changing visibility conditions during the morning commute. Fog of that density can collapse sight lines fast on valley roads, particularly on the highway corridors running through the flatlands north and east of town.
Forecasters said the fog was expected to begin dissipating after 9 a.m. No accidents or road closures were reported in connection with the advisory.