El Nino history, facts & predictions

San Francisco Rainfall During El Nino Years

  • El Nino episodes can range from weak to very strong. San Francisco recorded above normal rainfall for most strong and very strong years. The one exception was the strong El Nino in 1965-1966 (annual rainfall was just over 16 inches). The two strong El Ninos in 1982/1983 and 1997/1998 were associated with high rainfall totals. The last very strong El Nino in the 90s left its mark with nearly twice as much rain in an average year.

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Winter Outlook from Climate Prediction Center - Issued October 11, 2015

El Nino is playing a big role in the 2015-2016 Winter Outlook. The highest chance of above normal precipitation is focused in Southern California. The strength of the current El Nino is pushing the higher chances further north, closer to the Bay Area. Equal chances of above normal/or below normal precipitation is limited to the northern portions of the state.

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El Nino Regions

  • El Nino is not related to the coastal waters adjacent to the Bay Area. The area of interest is focused in the Equatorial Pacific. There are different El Nino regions... Nino 3, Nino 4, and a shared area of 3.4.  Most measurements of water temperature are made in the 3.4 region.  This is the region forecasters examine to determine El Nino status.

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Jet Stream

  • The energy released from the El Nino (warmer than normal temperatures in the equatorial Pacific) can fuel a storm track – and – direct it toward the Bay Area. The position and focus of the jet stream determines where the most intense precipitation falls. During El Nino events, the jet stream tends to focused in the southern half of the state.

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El Nino Fact Sheet

  • Graphic provides a general overview of El Nino. El Nino is not a storm. El Nino will not guarantee significant rain or snow for the upcoming winter. El Nino can change the storm track, increasing our chances for stormy weather this winter.

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Sierra Snow 

  • The two very strong El Ninos have produced above normal snowfall in the Sierra. The biggest wildcard this season will be snow levels. Whether we get rain or snow is the unknown. Temperatures are forecasted to be above normal this winter. Each storm is unique.  At this point, it is uncertain whether we will have more cold or warm storms.

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Panels Showing El Nino Strengthening 

  • The waters in the equatorial Pacific have been warming all year. The brighter colors indicate a strengthening El Nino in 2015. The most recent images show a pattern that resembles the last very strong El Nino during the winter of 1997/1998.


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