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Key findings

  • The highest monthly average temperature in Decatur for August is 78.1 degrees
  • The lowest monthly average temperature in Decatur for February is 29.4 degrees
  • The most monthly precipitation in Decatur occurs in June with 8.1 inches
  • The air quality index in Decatur is 12% better than the national average
  • The pollution index in Decatur is 86% better than the national average

Compare Decatur, IL Weather

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      Decatur Average Temperature

      In the event that the weather data was unavailable for this city, estimates based upon nearby cities were used.
      MonthTemp. (min)Temp. (max)Temp. (avg)Precipitation
      January24°F38°F31°F6.8"
      February23°F37°F29°F3.4"
      March35°F56°F45°F3.0"
      April43°F65°F54°F4.2"
      May54°F78°F66°F3.1"
      June64°F86°F75°F8.1"
      July65°F86°F76°F4.0"
      August68°F89°F78°F3.9"
      September59°F85°F72°F7.7"
      October49°F71°F60°F7.1"
      November37°F56°F45°F6.1"
      December24°F37°F30°F2.5"

      Decatur air quality index & pollution index

      In the event that the air quality/pollution data was unavailable for this city, estimates based upon nearby cities were used.
      IndexDecaturIllinoisNational
      Air quality index444150
      Pollution index703,2183,347,2955,066,862

      Decatur air quality information

      MeasurementTotal
      Days measured365
      Days with good air quality255
      Days with moderate air quality110
      Days w/ poor A.Q. for sensitive groups0
      Days with unhealthy air quality0

      Decatur air quality information

      PollutantTotal
      Arsenic0.001%
      Benzene0.020%
      Carbon Tetrachloride0.000%
      Lead0.000%
      Mercury0.000%

      Average monthly Decatur temperature with heat index

      Decatur monthly precipitation with daily maximum

      Decatur monthly snow depth with daily maximum

      Decatur monthly wind speed information

      Nearby cities with good air quality

      City, StatePopulationAir Quality IndexNational Avg.
      Dalton City, IL4744412%
      LaPlace, IL1614412%
      Niantic, IL5304412%
      Forsyth, IL3,4214412%
      Maroa, IL1,7244412%
      Decatur, IL74,0634412%

      Cities with similar population

      City, StatePopulationAir Quality IndexNational Avg.
      Gastonia, NC73,8773628%
      Bolingbrook, IL74,3205510%
      San Ramon, CA74,3664020%
      Schaumburg, IL74,3665510%
      Perris, CA73,7188978%
      Decatur, IL74,0634412%
      Source: The Decatur, IL weather data displayed above is derived from the NOAA (National Oceanic and Atmospheric). Air quality and pollution data is derived from the EPA (United States Environmental Protection Agency). Air quality and pollution levels measured in a particular area may not be representative of the entire county.