Massac County Climate
Massac County, Illinois
Avg Annual Temp
57.3°F
Annual Precip
50.2"
Annual Snowfall
3.1"
Extreme Heat Days
41.5
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Massac County Weather
A Warm Southern Illinois Climate Profile
Massac County is significantly warmer than the national median with an annual average of 57.3°F. It experiences a humid subtropical influence that is rare for the rest of the state.
One of Illinois' Warmest and Wettest
Massac's 57.3°F average far exceeds the state average of 52.8°F, placing it among the warmest Illinois counties. It also receives 50.2 inches of rain, well above the state's 41.7-inch norm.
Vastly Different Weather Than Northern Peers
Compared to northern counties like McHenry, Massac sees almost no snow, averaging just 3.1 inches annually. It also endures 42 days of extreme heat, the highest in this regional set.
Mild Winters and Intense Summer Heat
The county sees a sweltering 42 days above 90°F, with July averages reaching 78.4°F. Winters are much milder than the rest of Illinois, staying well above freezing with a 36.6°F average.
Prioritize Cooling and Storm Preparedness
High-capacity air conditioning is vital to handle the six weeks of extreme heat days. Because the county receives over 50 inches of rain, ensure your property has excellent drainage and gutter systems.
Frequently Asked Questions
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Data source: NOAA National Centers for Environmental Information (NCEI), U.S. Climate Normals 1991-2020.
Climate normals are 30-year averages of weather variables computed from 1991 to 2020. Station data is aggregated to county level using spatial averaging. Data is informational only — not a substitute for official National Weather Service forecasts or emergency weather warnings.