TODAY MAY09
TEMPERATURE67
HUMIDITY40
PRESSURE29.98
WIND COND.360 20.5
  • 9154Mon
  • 9250Tue
  • 8749Wed
  • 8549Thu
  • 8348Fri
daynightWeather update from Santa Rosa, Santa Rosa Sonoma County Airport at

Key findings

  • The highest monthly average temperature in St. Helena for July is 64.9 degrees
  • The lowest monthly average temperature in St. Helena for December is 46.1 degrees
  • The most monthly precipitation in St. Helena occurs in December with 6.9 inches
  • The air quality index in St. Helena is 32% better than the national average
  • The pollution index in St. Helena is 56% worse than the national average

Compare St. Helena, CA Weather

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      St. Helena 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
      January36°F60°F46°F6.0"
      February39°F64°F50°F5.7"
      March41°F67°F52°F4.6"
      April43°F71°F55°F2.4"
      May46°F77°F60°F1.1"
      June50°F83°F64°F0.4"
      July52°F85°F65°F0.0"
      August52°F84°F64°F0.0"
      September49°F85°F64°F0.2"
      October46°F78°F59°F2.0"
      November41°F67°F52°F3.2"
      December36°F59°F46°F6.9"

      St. Helena 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.
      IndexSt. HelenaCaliforniaNational
      Air quality index345550
      Pollution index7,898,29018,106,7265,066,862

      St. Helena air quality information

      MeasurementTotal
      Days measured365
      Days with good air quality346
      Days with moderate air quality18
      Days w/ poor A.Q. for sensitive groups0
      Days with unhealthy air quality1

      St. Helena air quality information

      PollutantTotal
      Arsenic0.260%
      Benzene0.080%
      Carbon Tetrachloride0.005%
      Lead0.240%
      Mercury0.270%

      Average monthly St. Helena temperature with heat index

      St. Helena monthly precipitation with daily maximum

      St. Helena monthly snow depth with daily maximum

      St. Helena monthly wind speed information

      Nearby cities with good air quality

      City, StatePopulationAir Quality IndexNational Avg.
      Calistoga, CA5,2813432%
      Cotati, CA7,4153432%
      Penngrove, CA2,9403432%
      Santa Rosa, CA173,1653432%
      Angwin, CA3,5053432%
      St. Helena, CA5,9953432%

      Cities with similar population

      City, StatePopulationAir Quality IndexNational Avg.
      Brookville, OH5,993476%
      Deschutes River Woods, OR5,9932060%
      Bowleys Quarters, MD5,998468%
      Erwin, TN5,9984510%
      Ranchettes, WY6,0004314%
      St. Helena, CA5,9953432%
      Source: The St. Helena, 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.