Washington County Climate
Washington County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
55.1°F
Annual Precip
42.2"
Annual Snowfall
11.7"
Extreme Heat Days
31
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
6b
Minimum winter temperature range for plant survival
4,027
Excellent for heat-loving crops
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Washington County
Climate Verdict
Washington County has a mild, with an average annual temperature of 55.1°F, moderately wet with 42.2 inches of annual precipitation, occasional hot days — 31.2 per year above 90°F, light snow averaging 11.7 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are cold, with January averaging 30.0°F. summers are warm — July averages 77.2°F. The 47°F seasonal variation provides noticeable but manageable change.
Outdoor & Gardening Guidance
The moderate temperatures support hiking, cycling, and camping comfortably in spring, summer, and fall.
Regional Context
Washington County closely matches the Illinois statewide average temperature of 52.8°F.
Climate Profile
About Washington County Weather
A classic humid subtropical transition
Washington County averages 55.1°F annually, trending warmer than the national median. It receives 42.2 inches of precipitation, typical for the moist eastern half of the United States.
Above the Illinois state average
The county's 55.1°F average temperature is higher than the state mean of 52.8°F. It represents the warmer climate of southern Illinois, where winters are shorter and summers are more intense.
Drier than its eastern neighbors
While Washington is warm, its 42.2 inches of rain is lower than Wayne County's 46.5 inches. However, it experiences 31 days of extreme heat, significantly more than counties further north.
Hot summers and light snow
July averages a warm 77.2°F, contributing to a month's worth of days over 90°F. Winters are relatively mild, with only 11.7 inches of annual snowfall compared to much higher totals in northern Illinois.
Prepare for frequent summer heat
Air conditioning systems must be robust to handle 31 days of extreme heat each year. For winter, lightweight snow removal tools are usually sufficient for the modest 11.7 inches of snow.
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.