Jefferson County Climate
Jefferson County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
54.5°F
Annual Precip
44.9"
Annual Snowfall
9.5"
Extreme Heat Days
21
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
6b
Minimum winter temperature range for plant survival
3,832
Supports most vegetables & fruits
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Jefferson County
Climate Verdict
Jefferson County has a mild, with an average annual temperature of 54.5°F, moderately wet with 44.9 inches of annual precipitation, occasional hot days — 20.7 per year above 90°F, light snow averaging 9.5 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are cold, with January averaging 30.1°F. summers are warm — July averages 76.5°F. The 46°F seasonal variation provides noticeable but manageable change.
Outdoor & Gardening Guidance
Growing season and gardening data is currently limited for Jefferson County. Check the USDA Plant Hardiness Zone Map and local extension office for specific guidance.
Regional Context
Jefferson County closely matches the Illinois statewide average temperature of 52.8°F, it is somewhat wetter than average for Illinois.
Climate Profile
About Jefferson County Weather
Warmer than the national median temperature
Jefferson's 54.5°F average temperature is higher than the national median of 53°F. It experiences a relatively wet climate with 44.9 inches of rain.
Exceeding the Illinois state temperature average
At 54.5°F, the county is 1.7°F warmer than the Illinois state average of 52.8°F. It sits firmly in the warmer southern half of the state.
Much less snow than northern Henry County
Jefferson sees only 9.5 inches of snow, nearly 20 inches less than Henry County. Its precipitation is also higher than the state average of 41.7 inches.
Warm summers with three weeks of heat
July averages 76.5°F, including 21 days of extreme heat above 90°F. Winters are relatively mild, with January temperatures averaging 30.1°F.
Focus on cooling and heavy rain management
Efficient air conditioning is key for the 21 extreme heat days. Residents should also be prepared for 44.9 inches of rain with proper roof and gutter care.
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.