SEATTLE -- Thick fog slowed traffic during Monday morning's commute but was causing no significant delays at Sea-Tac Airport.

Washington State Ferries said there were some delays due to fog on ferry runs between Bremerton and Seattle and between Bainbridge Island and Seattle.

Fog cut visibility to about a quarter mile, making for a tricky drive, said reporter Jeff Dubois.

Dubois said there was heavy fog on Interstate 90 on the Eastside and on I-5 into Seattle. Along Highway 99 in SeaTac, headlights seemed to appear out of nowhere and taillights disappeared in the fog.

At SeaTac, most flights were on time. Get the latest flight information here.

Forecasters said a large ridge of high pressure will keep Western Washington dry, with morning fog giving way to a partly sunny afternoon.