San Juan County Climate
San Juan County, Washington
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
50.8°F
Annual Precip
23.8"
Annual Snowfall
5.8"
Extreme Heat Days
0
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
9a
Minimum winter temperature range for plant survival
1,493
Limited to cold-tolerant varieties
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: San Juan County
Climate Verdict
San Juan County has a mild, with an average annual temperature of 50.8°F, semi-arid conditions with only 23.8 inches of annual precipitation, rare extreme heat with only 0.3 days above 90°F annually, light snow averaging 5.8 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are mild, with January temperatures averaging 41.5°F. summers are pleasantly cool with July averaging 61.5°F. The climate is remarkably stable year-round, with only a 20°F difference between January and July. December is typically the coldest month and August the warmest.
Outdoor & Gardening Guidance
Growing season and gardening data is currently limited for San Juan County. Check the USDA Plant Hardiness Zone Map and local extension office for specific guidance.
Regional Context
San Juan County closely matches the Washington statewide average temperature of 49.9°F, it is also noticeably drier, receiving 14.7 inches less precipitation than the state average, the county experiences 17.69276705276705 fewer extreme heat days than the state average.
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 sources: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020. Forecast and alert data from National Weather Service API. Air quality data from Open-Meteo.
Climate normals are 30-year averages of weather variables. Station data is aggregated to county level. Forecasts and alerts are fetched live and may change frequently. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.