Dense Fog Advisory in Effect: Affected Areas, Hazardous Commute Hours, and Must-Know Safety Tips

The National Weather Service has expanded Dense Fog Advisories across the Pacific Northwest for Thursday, February 5, warning that visibility could drop to a quarter-mile or less during the early-morning hours. IMPACT ZONES • Puget Sound lowlands—including Seattle, Tacoma, Everett, Bremerton and Olympia—are under advisory until 9 a.m. as cool, calm conditions trap moisture at the surface. • Farther south, East-Central Willamette Valley and the Lane County lowlands of Oregon remain under a similar alert until 11 a.m.. • Drivers on Interstates 5, 90 and 405, as well as regional highways 99, 101 and 18, should prepare for abrupt drops in visibility and slick pavement caused by fog condensation. WHY THIS HAPPENS Overnight radiational cooling, light winds and lingering ground moisture allow tiny water droplets to suspend in the air, creating a thick, ground-hugging cloud layer. When visibility sinks to ¼ mile or less for a large area, the NWS issues a Dense Fog Advisory. MORNING COMMUTE & TRAVEL • Slow down, keep headlights on low beam and leave extra stopping distance. • Use fog lights where available; avoid high beams that reflect off droplets and worsen glare. • Expect delayed ferry departures on Puget Sound and possible flight hold-and-release programs at Sea-Tac and Portland International airports as air-traffic controllers space out arrivals. HEALTH & AIR-QUALITY NOTE Stagnant air beneath the fog layer can trap pollutants, pushing Air Quality Index values into the “Moderate” category in valley locations. Residents with asthma or other respiratory issues should limit strenuous outdoor activity until mixing winds return later today. LOOKING AHEAD Forecasters expect the fog to thin between 9 a.m. and noon as daytime heating and a weak onshore breeze mix the lower atmosphere. Sunshine will follow, but patchy fog could redevelop overnight where skies stay clear and winds remain light. BOTTOM LINE If you must hit the road before the fog lifts, budget extra time, drive defensively and stay tuned to NOAA Weather Radio or local alerts for any extensions of the Dense Fog Advisory.