U.S. scientists say satellite observation show a neutral near-normal sea-surface height condition dubbed "La Nada" has stubbornly persisted for 16 months.

The National Weather Service's Climate Prediction Center said models suggest this pattern will continue through the spring of 2014.

"Without an El Nino or La Nina signal present, other, less predictable, climatic factors will govern fall, winter and spring weather conditions," climatologist Bill Patzert of NASA's Jet Propulsion Laboratory, in Pasadena, Calif., said.

"Long-range forecasts are most successful during El Nino and La Nina episodes. The 'in between' ocean state, La Nada, is the dominant condition, and is frustrating for long-range forecasters. It's like driving without a decent road map -- it makes forecasting difficult."

Some of the wettest and driest winters of the last several decades have occurred during La Nada periods, scientists said.

"Neutral infers something benign, but in fact if you look at these La Nada years when neither El Nino nor La Nina are present, they can be the most volatile and punishing," Patzert said. "As an example, the continuing, deepening drought in the American West is far from 'neutral.'"

For the past several decades about half of all years have experienced La Nada conditions, compared with about 20 percent for El Nino and 30 percent for La Nina, a JPL release said Monday.