Opposite Extremes in Southern California’s Wet Season
Alex Tardy, NOAA National Weather Service, San Diego, San Diego, CA
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Abstract
The fall of 2015 brought significant anticipation of an above normal precipitation season which could greatly improve the worse drought in modern history which began in 2012.  By December 2015, the strongest El Niño episode, equal in intensity to 1997-98 season, had formed in the equatorial Pacific Ocean. The National Weather Service forecast was for the highest probability of occurrence to be above normal precipitation for most of California.  Despite the strong El Nino persisting through late winter and the Pacific Jet stream significantly enhanced and consolidated the impact of precipitation was mostly kept well north of Southern California resulting in the 5th consecutive year of below normal precipitation and no improvement to the drought.

In 2016, California entered the cool season with widespread drought conditions and a developing La Niña episode in the equatorial Pacific.  The forecasts again followed the general analogs of either slightly drier than normal probabilities for Southern California, or equal chances of all 3 potential outcomes across most of California. The expectations were not to make significant progress on the historical drought and low water supplies.  The water year starting October 1, 2016 through February 2017 was the wettest in California history and resulted in snowpack and precipitation near the all-time 1982-83 season.  By March 1st, all areas in California had reached or exceeded their annual precipitation and were 150 to 200 percent of normal.  Across southern California, major impacts occurred from storms in January and February, resulting in hundreds of downed trees, flash flooding, the 3rd highest recorded water level on the San Diego River and millions of dollars in damage.  For California, the abundant precipitation led to flooding and damage to reservoir infrastructure, and most importantly up to 5 category improvement on the drought.

This presentation will discuss the climatological extremes, impacts and decision support services provided to partners during these unprecedented weather events.