Monmouth, IL Climate

Climate Insight: Monmouth, IL

An annual average temperature of 51°F, ranging from a mean daily high of 61°F to a mean daily low of 41°F is what the NOAA 1991–2020 climate normals report for Monmouth, Illinois. July is typically the warmest month of the year, while January is the coldest. That baseline comes from 2 weather stations and thirty years of averaging, so it reflects a typical month rather than any one year's swings.

Monmouth averages 39.4 inches of precipitation a year, with 25.6 inches typically falling as snow, and that matters as much to daily life here as temperature does. The frost-free season averages 176 days, which directly shapes the planting calendar and growing potential for the area, with the last spring freeze near April 22 and the first fall freeze near October 15. As for energy demand, 6,099 heating degree days and 891 cooling degree days tell the story of how often furnaces and air conditioners run during a normal year.

On PlainClimate's composite comfort index, Monmouth scores 59/100 (Moderate), a blended measure that weighs temperature mildness, precipitation moderation, and extreme-weather frequency against one another. Shoulder seasons bring the mildest highs and lows in the monthly tables above, summer brings July-driven heat, and winter brings January-driven cold - use that rhythm for planning. These figures are thirty-year averages rather than forecasts, so a specific year may still run warmer, cooler, wetter, or drier than what's shown.