SACRAMENTO — As robust storms continue to move through California, El Nino conditions in the Pacific Ocean are already starting to weaken, a National Weather Service expert says.

Sea surface temperatures in the equatorial Pacific that serve as a key fuel for the weather phenomenon are starting to cool, although a strong El Nino is expected to persist in the Northern Hemisphere through the winter, said Michelle Mead, a National Weather Service warning coordinator.

The current weather pattern, fed by a dominant subtropical southern jet stream, is typical for a strong El Nino winter, Mead said in an email. But uncertainty is emerging as to whether the pattern will remain for the entire winter, particularly for Northern California, she said.

“The precipitation and snowpack for this winter are still going to be storm-by-storm dependent,” Mead said. “As we’ve stated before, even an average winter will not save us from a four-year deficit.”

Sea-surface and atmospheric conditions are expected to return to neutral by late spring or early summer, marking an end to the current El Nino.

The update comes as a steady stream of storms have been pelting California since late fall, giving the Sierra Nevada 103 percent of its normal snowpack as of Jan. 11. However, the mountains have still only accumulated 45 percent of their average snowpack for April 1, according to the state Department of Water Resources.

In addition, many areas are struggling to maintain average seasonal precipitation. For instance, Redding has sopped up 4.7 inches of rain for the month as of Jan. 12, well above its normal 2.2 inches for the period, but its 14.57 inches since Oct. 1 is slightly behind its average of 15.05 inches, according to the National Weather Service.

Sacramento’s 5.71 inches of rain since Oct. 1 is well behind its normal 7.56 inches for the period, the weather service reports.

Reservoirs, too, have a ways to go. Shasta Lake, the federal Central Valley Project’s biggest reservoir, was holding only 33 percent of its capacity and 52 percent of its historical average on Jan. 11, while the State Water Project’s Lake Oroville was at 30 percent of capacity and 48 percent of normal for the date, the DWR’s California Data Exchange Center reported.

Mead and other federal and state officials have frequently sought to tamp down expectations for this winter after four years of drought, even while noting that this winter’s El Nino could rank among the three strongest since 1950.

Last week, Mead sent an email warning news organizations not to trust social media reports that forecasters were expecting as much as 15 inches of rain in 16 days in Northern California.

As it is, the federal Climate Prediction Center expects warmer temperatures and above-average precipitation throughout the West Coast in the next two weeks, with most of California seeing above-average chances of rainfall over the next three months.