Union County Climate
Union County, Illinois
NOAA NCEI 1991-2020 Climate NormalsAvg Annual Temp
58.5°F
Annual Precip
51.1"
Annual Snowfall
10.4"
Extreme Heat Days
43
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Growing Season & Gardening
7a
Minimum winter temperature range for plant survival
4,627
Excellent for heat-loving crops
Seasonal Overview
National Comparison
7-Day Outlook
Forecast
Current Conditions
Air Quality
Safety
Weather Alerts
Climate Advisory: Union County
Climate Verdict
Union County has a mild, with an average annual temperature of 58.5°F, moderately wet with 51.1 inches of annual precipitation, occasional hot days — 43 per year above 90°F, light snow averaging 10.4 inches per year. This climate profile shapes everything from energy costs to outdoor recreation opportunities.
Seasonal Breakdown
Winters are cold, with January averaging 35.3°F. summers are warm — July averages 79.2°F. The 44°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
Union County is 5.7°F warmer than the Illinois statewide average of 52.8°F, it is also noticeably wetter, receiving 9.4 inches more precipitation than the state average, the county experiences 15.738967803030302 more extreme heat days than the state average.
Climate Profile
About Union County Weather
Far Exceeding National Temperatures
Union County averages 58.5°F annually, which is nearly six degrees warmer than the national median. It features a humid subtropical influence unique to the state's southern tip.
Illinois’ Warmest and Wettest Corner
At 58.5°F, this is one of the warmest counties in Illinois, far exceeding the 52.8°F state average. It is also exceptionally wet, receiving 51.1 inches of annual rain.
A Southern Illinois Thermal Peak
Union is even warmer than St. Clair County, which averages 56.8°F. It also receives about eight more inches of rain annually than its northern neighbors.
Long Summers and Little Snow
The county faces 43 days of extreme heat with July temperatures averaging 79.2°F. Winters are the mildest in the state, averaging 37.9°F with only 10.4 inches of snow.
Manage Heat and High Humidity
Residents need high-capacity cooling and dehumidification to handle the 51.1 inches of rain and 43 days of extreme heat. Heavy winter clothing is rarely needed given the mild 37.9°F winter average.
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.