Washington County Climate
Washington County, Illinois
Avg Annual Temp
55.1°F
Annual Precip
42.2"
Annual Snowfall
11.7"
Extreme Heat Days
31.2
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About Washington County Weather
A classic humid subtropical transition
Washington County averages 55.1°F annually, trending warmer than the national median. It receives 42.2 inches of precipitation, typical for the moist eastern half of the United States.
Above the Illinois state average
The county's 55.1°F average temperature is higher than the state mean of 52.8°F. It represents the warmer climate of southern Illinois, where winters are shorter and summers are more intense.
Drier than its eastern neighbors
While Washington is warm, its 42.2 inches of rain is lower than Wayne County's 46.5 inches. However, it experiences 31 days of extreme heat, significantly more than counties further north.
Hot summers and light snow
July averages a warm 77.2°F, contributing to a month's worth of days over 90°F. Winters are relatively mild, with only 11.7 inches of annual snowfall compared to much higher totals in northern Illinois.
Prepare for frequent summer heat
Air conditioning systems must be robust to handle 31 days of extreme heat each year. For winter, lightweight snow removal tools are usually sufficient for the modest 11.7 inches of snow.
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.