Stephen Baxter, a meteorologist with NOAA's Climate Prediction Center, told reporters in May that La Nina temperatures are likely to begin developing this summer, and that there is a 75 percent chance of La Nina conditions by the end of the year.
And La Nina conditions historically bring less rain to much of California than El Nino or neutral conditions. So, the drought could drag on, or even worsen.
Mark Cowin, director of the California Department of Water Resources, told The New York Times, the state is "just one dry winter away from returning to where we were," despite the fact that drought conditions have greatly eased in some California communities.
This is not guaranteed, and some meteorologists have said anything can happen with La Nina this year.
"Climatology has its limitations as far as what the impact will be from a La Nina or an El Nino," said Jan Null, a meteorologist based in Northern California, who runs Golden Gate Weather Services. "The climatology is not a forecast," in the way that a short-term weather report is a forecast, he added, saying that many people mistook climatological predictions for El Nino as forecasts of what would happen, rather than as averages of the full range of possible scenarios.
"On average, Southern California tends to be dry, and the northern half of the state tends to be a toss up between wet and dry years. We had a strong La Nina in '73/'74, which was very wet in California. Two years later, '75/'76, we also had a strong La Nina, and it was the first year of the two-year drought, in the '70s. But if we go back to averages, it tends to be wetter in the Pacific Northwest and drier and drier as you go further south."
Correction: Jake Crouch is a scientist with the National Centers for Environmental Information at the National Oceanographic and Atmospheric Administration. Jan Null runs Golden Gate Weather Services. An earlier version misstated the names of the organizations.