It may be possible to predict some El Niños a year in advance—here’s why it matters

Why forecasts have limits

Forecasting models use observations of ocean temperatures, currents, winds and humidity to simulate future ocean and atmospheric conditions. But weather is sensitive to small changes in its starting conditions, making reliable forecasts beyond a week or two difficult.

Because the ocean changes more slowly than the atmosphere, El Niño and La Niña can generally be forecast further ahead. These events typically peak around December and can be predicted about six months in advance. Forecasts made from March to May, however, are notoriously unreliable.

Testing early predictions

The research team examined whether some forecasts could overcome the uncertainty of the March-to-May period. It analysed 7,500 forecasts produced by nine models developed in different countries. Researchers grouped forecasts by Pacific conditions at the time they began: La Niña, El Niño or neutral. They then checked whether the early predictions came true and looked for patterns in their accuracy.

La Niña offered a clue

Forecasts that started during La Niña were most successful at predicting conditions a year later. Those begun during neutral conditions were very likely to be wrong. The pattern appeared across all nine models. The researchers said La Niña conditions may have a stabilising influence, making predictions more reliable in those circumstances.