San Juan County Climate
San Juan County, Washington
Avg Annual Temp
50.8°F
Annual Precip
23.8"
Annual Snowfall
5.8"
Extreme Heat Days
0.3
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About San Juan County Weather
The Gentle Climate of the Islands
San Juan County averages 50.8°F annually, remaining cooler than the national median. Located in a rain shadow, it receives only 23.8 inches of annual precipitation, making it much drier than most coastal regions.
Warmer and Drier than the Mainland
The county's 50.8°F average annual temperature is slightly higher than the state average of 49.9°F. Its 23.8 inches of rain is remarkably low compared to the Washington average of 38.5 inches.
Drier Skies Compared to Skagit County
While Skagit County receives 57.9 inches of rain, the San Juan Islands receive less than half that amount. The surrounding waters insulate the islands, keeping winters milder than the nearby mainland.
Zero Extreme Heat and Mild Winters
The county records zero days of extreme heat over 90°F, with July temperatures averaging 61.5°F. Winters are similarly gentle, with a January average of 41.5°F and only 5.8 inches of annual snow.
Focus on Water Conservation and Light Layers
Air conditioning is virtually unnecessary here given the total lack of extreme heat days. Instead, residents should plan for water conservation during dry summers and keep light layers ready for the consistently mild, maritime air.
Frequently Asked Questions
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.