Oregon wakes up under a trapped lid of cold air, where frost coats windshields and fog hangs low over quiet streets. The air feels heavy and still, with little movement to clear it out.
An Air Stagnation Advisory remains in effect until noon Friday for Eugene, Portland, and much of the Willamette Valley. Light winds and limited mixing allow cold air and pollutants to settle near the ground. Air quality may slowly deteriorate, especially during morning and evening hours.
Early today, temperatures sit in the mid-20s with mist and freezing fog. Visibility drops in spots, especially near river valleys and open fields. Drivers should expect slick pavement from frost and patchy freezing fog during the morning commute. Allow extra travel time and use low-beam headlights in fog.
By midday, partial sunshine helps temperatures climb into the mid-40s. That improvement is temporary. Cold air quickly rebuilds after sunset, and fog redevelops. Residential wood burning is discouraged, as smoke can linger near ground level under stagnant conditions.
Thursday follows a similar pattern. Freezing fog forms early, then slowly clears late morning. Highs reach the mid-40s again. Thursday night brings renewed frost and fog, especially after midnight. Sensitive groups should limit prolonged outdoor exposure during poor air quality periods.
Friday brings gradual improvement. Sunshine becomes more dominant by afternoon, though frost still forms early. Highs stay near 45, with calmer travel conditions expected later in the day.
Looking ahead, the 6–10 day outlook shows near-normal temperatures for western Oregon. Precipitation chances increase next week, which may help clear lingering stagnant air.
Five-Day Outlook for Eugene, Oregon:
Today: Freezing fog early, partly sunny, high near 46.
Thursday: Dense freezing fog early, clearing late, high near 45.
Friday: Patchy fog early, sunny afternoon, high near 45.
Saturday: Frost early, mostly sunny, high near 46.
Sunday: Frost early, partly sunny, high near 48.
