Coos County has a marine climate – mild and humid – resulting from the moderating influences of the Pacific Ocean and from the rainfall induced by the Coast Range. Rainfall along the coast averages about 80 inches a year increasing inland with elevation to as much as 100 inches or more at points in the coast range. In Coos County, rainfall comes throughout the year with January, February, and March averaging about 7.4 inches per month. April, May, and June average 2.7 inches per month. July, August, and September average 1.0 inches per month. And October, November, and December average 7.2 inches per month.
Average maximum temperatures are 55°F with a 36°F average minimum temperature in January, February, and March. April, May, and June average temperatures are 64°F and 43°F. July, August, and September averages are 71°F with lows of 48°F. October, November, and December averages are 60°F with lows of 38°F. Extreme high or low temperatures are rare. Snowfall is also rare given the average elevation – Coos Bay at 10′ and North Bend at 16′ feet above sea level. And from March through October, the area is subject to prevailing winds from the northwest, and from November through February, winds come mainly from the southwest.
The growing season averages 200 days along the coast and in the river valley areas and decreases with higher elevation dropping to about 150 days along the eastern boundary of the county. Dates of last frost in spring and first frost in fall are not very useful because of the cool, rainy climate. Average late frost date in spring is March 30, and average first frost date in fall is October 30.
The elevation ranges from sea level on the west to over 3,600 feet in the coast range near the Douglas and Curry County boundaries. The soils and rainfall make the coastal mountains among the most productive timber areas in the world. For more information about soils, consult the Soil Survey of Coos County, Oregon which is available from the Natural Resources Conservation Service.