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Key findings

  • The highest monthly average temperature in Ontario for August is 78 degrees
  • The lowest monthly average temperature in Ontario for December is 55 degrees
  • The most monthly precipitation in Ontario occurs in December with 2.6 inches
  • The air quality index in Ontario is 79% worse than the national average
  • The pollution index in Ontario is 350% worse than the national average

Compare Ontario, CA Weather

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      Ontario 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
      January44°F69°F56°F2.3"
      February45°F70°F57°F2.0"
      March48°F74°F60°F1.2"
      April51°F77°F62°F0.7"
      May55°F81°F66°F0.4"
      June60°F88°F72°F0.0"
      July65°F94°F77°F0.1"
      August65°F95°F78°F0.0"
      September64°F93°F76°F0.2"
      October57°F84°F69°F0.4"
      November49°F77°F62°F0.6"
      December43°F68°F55°F2.6"

      Ontario 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.
      IndexOntarioCaliforniaNational
      Air quality index895550
      Pollution index22,790,90018,106,7265,066,862

      Ontario air quality information

      MeasurementTotal
      Days measured365
      Days with good air quality42
      Days with moderate air quality178
      Days w/ poor A.Q. for sensitive groups79
      Days with unhealthy air quality58

      Ontario air quality information

      PollutantTotal
      Arsenic0.060%
      Benzene0.190%
      Carbon Tetrachloride0.010%
      Lead0.220%
      Mercury0.230%

      Average monthly Ontario temperature with heat index

      Ontario monthly precipitation with daily maximum

      Ontario monthly snow depth with daily maximum

      Ontario monthly wind speed information

      Nearby cities with good air quality

      City, StatePopulationAir Quality IndexNational Avg.
      Citrus, CA11,7807244%
      West Covina, CA107,6347244%
      Azusa, CA48,4987244%
      South San Jose Hills, CA19,9147244%
      Jurupa Valley, CA100,7378978%
      Ontario, CA169,3898978%

      Cities with similar population

      City, StatePopulationAir Quality IndexNational Avg.
      Vancouver, WA169,9823824%
      Cape Coral, FL170,0633628%
      Sioux Falls, SD167,8843628%
      Jackson, MS172,0394412%
      Santa Rosa, CA173,1653432%
      Ontario, CA169,3898978%
      Source: The Ontario, CA 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.