Corvallis falls within the dry-summer temperate climate zone, also referred to as warm-summer Mediterranean . Temperatures are mild year round, with warm, dry, sunny summers and mild, wet winters with persistently overcast skies. Spring and fall are also moist seasons with varied cloudiness, and light rain falling for extended periods.
Winter snow is rare, but occasionally does fall, and amounts can range between a dusting and a few inches that do not persist on the ground for more than a day. The northwest hills will often experience more snow. During the midwinter months after extended periods of rain, thick, persistent fogs can form, sometimes lasting the entire day. This can severely reduce visibility to as low as 20 feet (6.1 m). The fog often persists until a new storm system enters the area. This fog could be seen as a type of tule fog.
Rainfall totals within the town itself are surprisingly variable, due to Corvallis lying right on the eastern edge of the Oregon Coast Range, with a small portion of the town inside of the range. Rainfall amounts can range from an average of 66.40 inches (168.7 cm) per year in the far northwest hills, compared to 43.66 inches (110.9 cm) per year at Oregon State University, which is located in the center of Corvallis.
Because of its close proximity to the coastal range, Corvallis can experience slightly cooler temperatures, particularly in the hills, than the rest of the Willamette Valley. The average annual low temperature is 4°F less than that of Portland just 85 miles (137 km) to the north. Despite this, temperatures dropping far below freezing are still a rare event.