St. Charles County Climate
St. Charles County, Missouri
Avg Annual Temp
55.5°F
Annual Precip
43.0"
Annual Snowfall
12.4"
Extreme Heat Days
38.25
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About St. Charles County Weather
Warm and Dynamic Regional Weather
St. Charles County averages 55.5°F annually, staying consistently warmer than the national median. This humid continental climate features robust precipitation and significant summer heat.
Outpacing the State Temperature Average
The county's 55.5°F average temperature ranks it slightly warmer than the Missouri state average of 54.9°F. Its precipitation level of 43.0 inches aligns almost perfectly with the state average of 43.8 inches.
The Warmer Edge of the Metro
St. Charles experiences more intense summer heat than counties to its north. It averages 38 extreme heat days per year, reflecting its position in the warming St. Louis metropolitan corridor.
Hot Summers and Moderate Winters
July brings an average temperature of 78.0°F, while January remains manageable at 30.5°F. The county receives 12.4 inches of snow annually, which is lower than the northern Missouri average.
Plan for Heat and Rapid Thaws
Outdoor activities require hydration strategies during the 38 annual days of 90°F heat. Homeowners should maintain gutters to handle the 43 inches of annual rainfall that often comes in heavy bursts.
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.