Grundy County Climate
Grundy County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
51.0°F
Annual Precip
38.0"
Annual Snowfall
21.5"
Extreme Heat Days
20
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
5b
Minimum winter temperature range for plant survival
3,344
Supports most vegetables & fruits
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Grundy County
Climate Verdict
Grundy County has a mild, with an average annual temperature of 51.0°F, moderate rainfall of 38.0 inches per year, occasional hot days — 20.1 per year above 90°F, moderate snowfall of 21.5 inches annually. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are very cold — January averages 23.9°F. summers are warm — July averages 75.0°F. Residents experience a substantial 51°F difference between winter and summer.
Outdoor & Gardening Guidance
Growing season and gardening data is currently limited for Grundy County. Check the USDA Plant Hardiness Zone Map and local extension office for specific guidance.
Regional Context
Grundy County closely matches the Illinois statewide average temperature of 52.8°F, it is somewhat drier than average for Illinois.
Climate Profile
About Grundy County Weather
Cooler Northern Continental Climate
Grundy County averages 51.0°F annually, placing it below the national median. This region is known for colder winters and brisk autumns.
Below the Illinois Average
The annual average of 51.0°F is nearly two degrees cooler than the state average of 52.8°F. This reflects the county's northern position and exposure to Great Lakes influences.
Low Precipitation for the Region
Grundy receives 38.0 inches of annual precipitation, which is lower than the 41.7-inch state average. It is one of the drier counties in the northern half of Illinois.
Snowy Winters and Warm Summers
Winters are significant with 21.5 inches of annual snowfall and a 23.9°F January average. Summers still bring 20 days of extreme heat where temperatures reach or exceed 90°F.
Invest in Winter Durability
The 21.5-inch snowfall average requires heavy-duty winter gear and effective home insulation. Residents should also prepare for the 20 annual heat days with reliable air conditioning.
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.