St. Clair County Climate
St. Clair County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
56.8°F
Annual Precip
43.0"
Annual Snowfall
12.2"
Extreme Heat Days
46
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
7a
Minimum winter temperature range for plant survival
4,344
Excellent for heat-loving crops
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: St. Clair County
Climate Verdict
St. Clair County has a mild, with an average annual temperature of 56.8°F, moderately wet with 43.0 inches of annual precipitation, occasional hot days — 46.1 per year above 90°F, light snow averaging 12.2 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are cold, with January averaging 32.4°F. summers are warm — July averages 78.9°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
St. Clair County is 4.0°F warmer than the Illinois statewide average of 52.8°F, the county experiences 18.838967803030304 more extreme heat days than the state average.
Climate Profile
About St. Clair County Weather
One of the Nation's Warmer Zones
St. Clair County averages a warm 56.8°F annually, far exceeding the national median of 52.7°F. This makes it one of the more temperate regions in the Midwest.
Topping the State Temperature Charts
The county is significantly warmer than the Illinois average of 52.8°F. It also receives 43.0 inches of rain, making it wetter than the state average of 41.7 inches.
The Heat of the Metro East
St. Clair is much hotter than Sangamon County, recording 46 extreme heat days compared to Sangamon’s 26. It represents a southern shift in climate for Illinois residents.
Sultry Summers and Light Snow
July averages a sweltering 78.9°F, leading to 46 days above 90°F annually. Winters remain mild by Illinois standards, with only 12.2 inches of annual snowfall.
Invest in Heavy-Duty Cooling
The frequency of extreme heat requires robust HVAC systems and heat-safety planning for outdoor workers. Minimal snow means residents can focus more on storm drainage than heavy plows.
Frequently Asked Questions
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Track your own weather in St. Clair County
Ambient Weather personal weather stations give you hyperlocal climate data.
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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.