Environment & Science

Strong El Niño likely means wet winter for Southern California, NOAA says

On October 15, 2015, NOAA's Climate Prediction Center released its outlook for precipitation and temperature for December through February and the drought outlook through January 31, 2016.
On October 15, 2015, NOAA's Climate Prediction Center released its outlook for precipitation and temperature for December through February and the drought outlook through January 31, 2016.
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The stretch between December and February is typically the wettest part of the year for California, and government forecasters said Thursday there's an above average chance that most of the drought-parched state, particularly Southern California, could see significant precipitation this winter.

Northern California — home to the all-important Sierra Nevada and its water-storing topography — should see average precipitation, which would be a welcome departure after four years of mostly bone-dry winters.

The big question, particularly for the Sierra, is whether that precipitation will fall as rain or snow. Forecasters with the National Oceanic and Atmospheric Administration (NOAA) said it's likely the Sierra region will be warmer than normal this winter.

“There’s a slightly higher probability for wetter-than-normal for Northern California and a better chance for Southern California. But for the north, where you’re concerned about water supply and filling reservoirs and building a snowpack, warmer conditions are not helpful,” said Alan Haynes, service coordination hydrologist for NOAA’s California Nevada River Forecast Center.

California typically relies on gradual melt water from the Sierra Nevada snowpack for 30 percent of its water. Less snow in the Sierra undercuts the mountains' natural water storage capacity. Even if more precipitation falls as rain this winter, Haynes said the state’s low reservoir levels would benefit from it.

“The reservoirs are so low that even if it just runs off, any precipitation we get in them will be welcome,” Haynes said. “The ideal situation would be that we fill them up and we build a nice snowpack too, which is possible. But the fact that we’re expecting a little warmer conditions, that’s not ideal.”

The  NOAA forecasters point to the strong El Niño climate pattern in the Central Pacific Ocean as central to the prediction for the wetter-than-average winter.  They say the amount of precipitation could even significantly loosen the grip of the drought from the Bay Area to the Mexican border. They cautioned, however, that it won't be enough to end the drought and that dry conditions could even intensify in Northern California.

“Although the winter outlook is good news for California, a wet winter is not guaranteed, and even a wetter than average winter is unlikely to erase four years of drought,” said Mike Halpert, deputy director of NOAA's Climate Prediction Center.

(Precipitation - U.S. Winter Outlook: 2015-2016. Credit: NOAA)

In the new winter weather outlook, officials with NOAA said this El Niño is likely to be among the three strongest since the 1950s, giving them increased confidence in predicting a wet winter for Central and Southern California.

“Probabilities this high are rare to see in a seasonal outlook. But despite higher than normal probabilities, none of the usual impacts are guaranteed, as the climate system is far more complicated than just El Niño, even a strong one,” Halpert said.

Halpert said seasonal outlooks are unable to predict the frequency and intensity of cold-air outbreaks and snowstorms.

Nationally, Southern Tier states are expected to see cooler, wetter weather, while those in the Northern Tier will most likely see above-average temperatures and drier conditions.

(Temperature - U.S. Winter Outlook: 2015-2016. Credit: NOAA)

This story has been updated.