Like the rest of the Willamette Valley, Corvallis falls within the Marine West Coast climate zone, with some Mediterranean characteristics. Temperatures are mild year round, with warm, dry sunny summers and mild, wet winters with persistent overcast skies. Spring and fall are also moist seasons with persistent cloudiness, and light rain falling for extended periods. Winter snow is rare, but occasionally does fall. Usually in the form of heavy wet snow, ranging between a dusting and a few inches that does not persist on the ground for more than a day. The northwest hills will often experience more snow. During the mid-winter 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 will often persist until a new storm system enters the area. This fog could be seen as a type of tule fog.

Rainfall total within the town itself is surprisingly variable. This is 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 [13] 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. Occasionally, rain can be seen falling in the northwest of the town, whereas it's just overcast, or even slightly sunny on the southeast portion of the town. This is due to the orographic lift of the prevailing cloud systems through the pacific northwest losing moisture and dissolving back into the air as it exits the coastal range.

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 degrees less than that of Portland just 85 miles (137 km) to the north. Despite this, temperatures dropping below freezing is still a rare event.