New forecasts show a higher chance for strong El Niño conditions this winter, increasing global temperatures and potentially giving the Bay Area a wetter-than-average rainy season.
The updated advisory by the U.S. Climate Prediction Network showed there is a 95% chance that El Niño conditions will extend through this winter into March. The center, operated under the National Oceanic and Atmospheric Administration, states that there is now a 71% of a “strong” El Niño, up from the 56% chance it predicted earlier this year.
“However, a strong El Niño does not necessarily equate to strong impacts locally, with the odds of related climate anomalies often lower than the chances of El Niño itself,” the center stated in its Sept. 14 update.
El Niño events are naturally occurring and cause parts of the Pacific Ocean near the equator to warm. This warming can affect weather patterns throughout the Earth by altering storm formation and movement.
In California, El Niño events generally cause wetter conditions in the south and drier conditions to the north, but that is not always what plays out. There have been 26 El Niño events in California since 1951, of which 11 were classified as “weak,” seven as “moderate,” five as “strong” and three as “very strong,” according to Jan Null, a meteorologist at Golden Gate Weather Services in Half Moon Bay.
While El Niño events can lead to wetter or drier conditions, Null states they are not consistent. In the Bay Area, eight of the 26 El Niño years resulted in below-normal rainfall, seven in normal rainfall of between 80% to 120% of average and 11 in about 120% of normal rainfall, according to Null.
“Think of it as the Pacific Ocean and the overlying atmosphere being on a performance-enhancing drug,” Null wrote on his website in an El Niño update earlier this year. “And just like we don’t know why an athlete will have a great performance one day and be mediocre the next, we don’t know whether a particular weather event during an El Niño or La Niña year would have occurred anyway.”
The last El Niño event was in 2018-2019. Marin County was hit by significant rainfall that caused flooding and damage, including a large mudslide in Sausalito that destroyed two buildings and injured a resident. The Marin Municipal Water District measured nearly 75 inches at Lake Lagunitas that year, above its average of 52 inches. That event was classified to be a “weak” El Niño.
The last “strong” El Niño occurred in 2015-2016, but predictions of a significant wet winter to end the state’s drought at the time never materialized. The Marin Municipal Water District only received 40 inches of rain that year.
Lucy Croy, the district water quality manager, said the agency’s historic rainfall records show El Niño events do result in wetter winters on average.
“El Niño seems to push us more toward having more rain. There were some big years,” Croy said, noting the 1997-1998 event when 90 inches of rain fell.
Following the significant rainfall this past winter, the outlook for Marin County’s water supply has become significantly more optimistic compared to the drought years of 2020 and 2021, when reservoirs reached alarmingly low levels. The seven local reservoirs operated by the Marin Municipal Water District were 87% full on Sunday, well above the 70% average for this time of year. Stafford Lake, the reservoir for the North Marin Water District in Novato, was 59% full as of Monday.
Both Marin agencies also receive supply from Sonoma Water. The agency reported its largest reservoir, Lake Sonoma, was at 92% of capacity, while the smaller Lake Mendocino was at about 72%.
Tony Williams, general manager of the North Marin Water District, which that serves Novato and parts of western Marin, said any above-normal rainfall is welcome, but he said there are also concerns about flooding.
“We would prefer a series of spaced-out rainfall events,” Williams wrote in an email. “We currently don’t plan to operate Stafford any differently than normal, meaning we plan to leave the lake at or near an elevation of 180 feet. Given the current status of Sonoma Water’s two reservoirs, we are heading into this winter in a really good situation regionally regardless of how potent El Niño is.”
