Stephenson County Climate
Stephenson County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
47.7°F
Annual Precip
38.4"
Annual Snowfall
34.5"
Extreme Heat Days
11
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
5a
Minimum winter temperature range for plant survival
2,811
Supports most vegetables & fruits
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Stephenson County
Climate Verdict
Stephenson County has a cool, averaging 47.7°F annually, moderate rainfall of 38.4 inches per year, rare extreme heat with only 10.6 days above 90°F annually, moderate snowfall of 34.5 inches annually. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are very cold — January averages 19.6°F. summers are warm — July averages 72.4°F. Residents experience a substantial 53°F difference between winter and summer.
Outdoor & Gardening Guidance
Growing season and gardening data is currently limited for Stephenson County. Check the USDA Plant Hardiness Zone Map and local extension office for specific guidance.
Regional Context
Stephenson County is 5.1°F cooler than the Illinois statewide average of 52.8°F, it is somewhat drier than average for Illinois, the county experiences 16.6610321969697 fewer extreme heat days than the state average.
Climate Profile
About Stephenson County Weather
A Cold Northern Climate
Stephenson County’s 47.7°F annual average is much lower than the national median of 52.7°F. This northern Illinois region experiences a true continental climate.
Well Below the State Average
The county is one of the coldest in Illinois, sitting five degrees below the state average of 52.8°F. It also records less rain than the state norm, with 38.4 inches annually.
Northern Chills Compared to Central IL
Stephenson is nearly six degrees cooler than Sangamon County on average. It receives 34.5 inches of snow, more than double the amount found in southern Illinois counties.
Brutal Winters and Mild Summers
Winter temperatures average a frigid 23.0°F, bringing heavy snowfall of 34.5 inches. Summers are pleasant, with only 11 days of extreme heat and a July average of 72.4°F.
Winter Readiness is Key
Residents must own heavy-duty snow removal equipment and ensure homes are well-insulated against the 23°F winter average. Air conditioning needs are lower here than in the rest of the state.
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.