PORTLAND, Ore. — Areas of dense fog are expected to form late Tuesday night and continue into Wednesday morning across portions of the Willamette Valley, with the greatest impacts likely south of Salem, forecasters said.
The National Weather Service in Portland warned that stretches of the I-5 corridor, including low-lying areas from Corvallis to Eugene, could see visibility drop below a quarter mile at times. Drivers are urged to allow extra time for the Wednesday morning commute and use caution on roadways where fog becomes locally dense.
Forecasters said fog development will not be uniform across the region. Easterly winds in the far eastern Portland and Vancouver metro area, including Troutdale, are expected to keep skies clear overnight and prevent fog formation there. In contrast, fog is more likely in the western Portland metro, particularly west of I-205, where calmer conditions favor rapid visibility reductions.
The NWS forecast graphic shows the highest fog probabilities—up to 60% near Eugene—while Salem has about a 13% chance and Portland closer to 18%. Coastal areas such as Tillamook and Lincoln City are expected to remain mostly clear with minimal fog risk.
If fog does develop, conditions may vary significantly over short distances, with some corridors experiencing sudden drops in visibility. Transportation officials advise motorists to slow down, increase following distance and use low-beam headlights when driving through fog.
The weather service said fog should gradually lift by mid to late Wednesday morning, giving way to improved travel conditions across the region.
