Weather Data for Island County

 
 

Weather data is collected here in Island County by approximately 50 volunteers for WSU Cooperative Extension. Longterm data shared in this summary was collecte by Burton Engle and his family in Coupeville during much of this century. Current up to date data is collected at the Sherman Farm by Don Sherman. Longterm Data for the Oak Harbor area is collected by Naval Air Station Whidbey. This data goes back to 1942 where-as the data for Coupeville reaches back to the late 1800's (1896)

General Overview of Island County Weather
Island County climate is highly influenced by the maritime air in our region. The Olympic Mountians create special conditions that alter the rainfall patterns considerably on Whidbey and to some extent on Camano Islands. A term is used to decribe this phenomenon "the rain shadow". The shadow effect is brought about by the fact that marine weather moves east off the Pacific Ocean and encounters the Olympic Mountains west of Island County. The marine air then moves around or is thrust upward to cooler temperatures dropping considerable moisture on the mountains themselves, hence drying the air prior to reaching Island County. The region just north of Coupeville (Pt. Partridge) is impacted by this action the most and is one of the driest areas in the county, approximately 18 to 19 inches per year on average. Annual rainfall around the islands will vary a great deal. Coupeville, the oldest recording site has an annual average over the past 100 years of approximately 20 inches. However, regions North and South have much higher rainfall levels. South Whidbey at Clinton ranges in the 30's and areas North of Oak Harbor can be in the high 20's. Camano Island generally ranges in the mid twenties to mid 30's. Seasonal rainfall patterns for the Puget Sound and Island County demonstrate summer draught during the months of July and August with Coupeville getting on average less than one inch per month. The wettest month for Coupeville and surrounding regions is typically December (Coupeville slightly less than 3 inches). Some measurable precipitation is likely 120 days of the year Temperatures can vary a great deal around the islands, however it is typical that temperatures are several degrees cooler on the islands than on the mainland of the Puget Sound region. At Coupeville average daily temperatures range from the low 70s in the heat of the summer to mid 30's for lows in the winter. Extremes have ranged from the high 90's to just above freezing during the year. Where you live on the islands can have a dramatic impact on air temperatures. Those who live along the shoreline will almost always have cooler summers and warmer winters, all moderated by the marine waters. This localized climatic variation can have significant impacts on the type of garden plants grown as well as landscape plant problems. Humidity is typically higher along the shoreline. Generally the last date of freezing temperatures for the islands is mid April and the first frost of the year is around the end of October.
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