"It is still true that La Niña tends to correlate with dry water years, which the National Weather Service defines as from Oct. 1 to Sept. 30. During La Niña, the sea surface temperatures of the central and eastern Pacific Ocean cool. And the jet stream - the west-to-east band of wind in the atmosphere - shifts northward. This typically pushes winter storms toward the Pacific Northwest and Canada, while leaving swaths of California drier than average, especially in the south."
"The 2016-17 La Niña season brought downtown L.A. 134% of its average annual rainfall. It was the second-wettest season in terms of statewide precipitation and single-handedly ended California's punishing five-year drought. So much rain fell that season that California's second-largest reservoir, Lake Oroville, spilled over its brim. Mass evacuations were ordered amid fears a key retaining wall could collapse, sending floodwaters rushing into communities below - a tragedy that was ultimately averted."
La Niña typically cools central and eastern Pacific sea surface temperatures and shifts the jet stream northward, which often routes winter storms into the Pacific Northwest and leaves parts of California drier. Historically, 15 of 25 La Niña events since 1954 brought drier-than-normal conditions to California, but La Niña does not always mean drought. Recent decades include several La Niña seasons that were extremely wet, notably 2010-11 and 2016-17. The 2016-17 season delivered well above-average rainfall, ended a multi-year drought, and triggered Lake Oroville overflow and evacuation fears during severe flooding.
Read at Los Angeles Times
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