TODAY MAR28
TEMPERATURE67
HUMIDITY26
PRESSURE101760
WIND COND.200 13
  • 7257Fri20%
  • 7555Sat30%30%
  • 7761Sun40%40%
  • 7652Mon40%70%
  • 6139Tue40%
daynightWeather update from St. Louis Downtown Airport at
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Weather Quick Facts

  • The highest monthly average temperature in O'Fallon for July is 77.9 degrees
  • The lowest monthly average temperature in O'Fallon for January is 31.8 degrees
  • The most monthly precipitation in O'Fallon occurs in April with 10.2 inches
  • The air quality index in O'Fallon is 28% worse than the national average
  • The pollution index in O'Fallon is 122% worse than the national average

Compare O'Fallon, IL Weather

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      O'Fallon 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
      January23°F42°F32°F5.6"
      February25°F45°F34°F3.8"
      March37°F59°F47°F7.1"
      April47°F70°F57°F10.2"
      May56°F77°F66°F8.9"
      June65°F87°F76°F9.2"
      July68°F89°F78°F8.0"
      August66°F88°F76°F7.8"
      September58°F82°F69°F8.4"
      October47°F70°F57°F8.6"
      November36°F57°F46°F6.9"
      December28°F45°F36°F8.2"

      O'Fallon 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.
      IndexO'FallonIllinoisNational
      Air quality index544142
      Pollution index6,055,6403,148,6942,726,193

      O'Fallon air quality information

      MeasurementTotal
      Days measured365
      Days with good air quality134
      Days with moderate air quality221
      Days w/ poor A.Q. for sensitive groups8
      Days with unhealthy air quality2

      O'Fallon air quality information

      PollutantTotal
      Arsenic0.010%
      Benzene0.070%
      Carbon Tetrachloride0.040%
      Lead0.100%
      Mercury0.230%

      Average monthly O'Fallon temperature with heat index

      O'Fallon monthly precipitation with daily maximum

      O'Fallon monthly snow depth with daily maximum

      O'Fallon monthly wind speed information

      Nearby cities with good air quality

      CityPopulationAir Quality IndexNational Avg.
      Glen Carbon, IL12,468548.0%
      Maryville, IL7,962548.0%
      Brooklyn, IL428548.0%
      Rentchler, IL4548.0%
      Summerfield, IL324548.0%
      O'Fallon, IL29,487548.0%

      Cities with similar population

      CityPopulationAir Quality IndexNational Avg.
      Crofton, MD29,482476.0%
      Austintown, OH29,4674216.0%
      Suisun City, CA29,4593530.0%
      Canton, GA29,459524.0%
      Seguin, TX29,458492.0%
      O'Fallon, IL29,487548.0%
      Source: The O'Fallon, 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.