La Niña? El Niño? Wet winter perplexes

Californians can be excused for being confused about the weather forecast.

- BY RONG-GONG LIN II

GINA FERAZZI Los Angeles Times

RECENT STORMS didn't bring much powder for ski resorts. Above, Snow Summit in Big Bear Lake.

Scientists in October said La Niña had arrived, which many associate with dry conditions, particularly in the Southland.

But we have instead experienced a very wet season — at least so far — with rain bringing much-needed moisture to the brush, probably putting an end to the autumn fire season, and helping to keep the state’s reservoirs in good shape.

So what is going on?

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.

Out of 25 La Niñas since 1954, 15 have brought drier-than-normal conditions to California.

But La Niña “doesn’t always mean drought,” said meteorologist Jan Null, an adjunct professor at San José State University.

In fact, out of the seven La Niñas seen over the last 15 years, three were whoppers when it came to rain.

Powerful storms pounded California throughout 2010-11, building a snowpack so epic that ski resorts actually complained.

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.