Portland starts Sunday, Nov. 1, in fog and mist, with temperatures in the low 40s. A Dense Fog Advisory remains in effect through 10 a.m., with visibility possibly falling to a quarter-mile or less in parts of the metro area. The fog is expected to fade by late morning, followed by mostly sunny skies and a high near 55. During the murkiest hours, drivers should slow down and leave extra space; pedestrians and cyclists may want bright or reflective clothing.
The fog fits a seasonal pattern, though the climate context does not verify the conditions in any particular neighborhood today. The National Weather Service Portland climate summary says lengthening autumn nights allow valleys to cool more, helping fog form on clear nights; it can be dense late at night and early in the morning and may persist for several days.
A brief sunny break before rain
Sunday night is forecast to turn partly cloudy, with patchy fog developing after 10 p.m. and a low near 40. Monday brings another foggy morning, then clouds and a high around 56. Tuesday is expected to be partly sunny, with a high near 60; patchy fog could return late Tuesday night as temperatures fall to about 43.
The first notable rain chance arrives Wednesday: areas of fog are forecast to give way to light rain later in the day, with light amounts likely Wednesday night. Thursday has a slight chance of rain before 4 p.m. and another likely round Thursday night. Friday is expected to be mostly cloudy, with rain likely before 4 p.m.; Saturday brings another chance of light rain and a high near 59.
As routine preparation for the coming rain—not a warning that this forecast will cause flooding—the Portland Bureau of Transportation advises residents to clear surface debris from storm drains they can safely reach from the curb, when possible. PBOT says not to stand in the street to clear a drain and never to lift a grate.
Fog is a visibility concern, but it does not by itself show that air quality is poor. The Oregon Department of Environmental Quality says DEQ and LRAPA issue air-quality advisories when inversions bring extended poor air quality; that is separate information from this fog forecast.
