California won’t emerge from its three-year drought even if most areas in the state receive average rainfall this winter, a federal climate expert said.

With its major reservoirs only holding about half the water they usually do at this time of year, the Golden State would need an exceptional precipitation year to bring them up to average, said Kevin Werner of the National Oceanic and Atmospheric Administration.

That’s not likely given the expectation of a weak El Nino weather pattern in the West, which could lead to a drier-than-normal winter for northern and central California, explained Werner, NOAA’s western regional climate services director.

“Winter precipitation is particularly important for that state, especially in the mountains,” he told reporters on Oct. 16, noting that mountain snowpack and river flows were significantly below normal at the end of last winter.

“The situation is not likely to change even if we get an average precipitation year,” Werner said. “We need an above-average precipitation year to bring our reservoirs up to normal, which is unlikely to happen with the current forecast.”

Werner added he expects California’s groundwater supplies to be “significantly if not severely depleted this year going forward,” providing “a diminishing resource” for growers and others who depend on it.

Werner’s remarks came as the climate center issued its annual winter outlook, which favors a warmer-than-average winter throughout the West and suggests the Pacific Northwest will see less rain and snow than in a typical winter.

Above-average rainfall is expected in the nation’s sun belt, from the southern half of California to Florida and up the Eastern seaboard, according to the outlook.

El Nino, an atmospheric change marked by the warming of surface waters in the tropical Pacific, faces about a two-thirds chance of developing this winter, federal forecasters say. But while strong El Nino conditions pull more moisture into California, this episode will probably offer little help.

“The winter impacts typically associated with weak El Nino episodes are not nearly as reliable as with strong events,” said Mike Halpert, the Climate Prediction Center’s acting director.

Most of central and northern California remains at equal chances of above-, at or below-normal precipitation over the next three months, according to the CPC. But even with a normal winter, recovery from the drought will be slow, Halpert said.

The state is unlikely to see a repeat of the blocking ridge that kept storms from entering California through most of last winter and into the spring, he said.

“The development of El Nino does not favor that type of ridge along the coast,” he said. “If there’s any type of ridge, it’ll be a little further to the north, which allows for precipitation in the central and southern parts of the state.”

NOAA also updated its U.S. Seasonal Drought Outlook on Oct. 16, predicting that drought conditions will ease in parts of California but develop or intensify in other parts of the West, including northeast Oregon, eastern Washington and parts of Idaho.

Recommended for you