McHenry County Climate
McHenry County, Illinois
Avg Annual Temp
48.6°F
Annual Precip
38.4"
Annual Snowfall
33.1"
Extreme Heat Days
16.133333333333333
days >= 90°F/yr
Monthly Temperature
Precipitation Calendar
Seasonal Overview
National Comparison
Climate Profile
About McHenry County Weather
Chilly Northern Climate and High Snow
McHenry County is notably cooler than the national average, with a mean temperature of 48.6°F. It serves as a classic example of a cold-winter humid continental climate.
One of the Coldest Illinois Counties
The average of 48.6°F is significantly lower than the Illinois state average of 52.8°F. McHenry ranks as one of the state's most northern and coldest regions.
The Snow Capital of the Region
With 33.1 inches of snow annually, McHenry receives over ten times more snowfall than southern Massac County. It also has the fewest extreme heat days in the group at just 16.
Long Winters and Mild Summers
Winter dominates here with a frigid December-February average of 24.8°F and heavy snow accumulation. Summers are pleasant and mild, with July averages peaking at only 72.9°F.
Invest in Heavy Winter Equipment
A high-quality snow blower is essential to manage the 33.1 inches of annual snowfall. Homeowners should also prioritize high-efficiency heating systems for the long, 21.8°F January nights.
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.