Long-range forecasts

Looking one or more months into the future

Our long-range (seasonal) forecasts provide information about atmospheric and oceanic conditions up to seven months into the future. They are produced every month with a 51-member ensemble at a horizontal resolution of around 36 km.

Annual forecasts are produced with the same system every three months and extend 13 months into the future.

Long-range charts include differences (or anomalies) from a long-term (model-based) climatology and probabilities of above normal, normal or below normal conditions.

Find out more about how our long-range forecasts are produced.


Our seasonal forecasting system (SEAS5)

Like the medium- and extended-range forecasts, our long-range forecasts are produced using the ECMWF Integrated Forecasting System (IFS) which uses an Earth system model to represent interactions between the atmosphere, ocean, land and other Earth-system components.

Our seasonal forecasting system uses modelling and initialisation methods which are very similar to ECMWF’s other ensemble forecasts, but the SEAS system is updated less frequently.

El Niño/La Niña forecasts and predictability in the long range

Long-term predictions rely on aspects of Earth system variability which have long timescales (months to years) and which are, to a certain extent, predictable. The most important of these is the El Niño/La Niña phenomenon.

El Niño refers to periods of anomalous warming in the tropical eastern Pacific (anomalous cooling periods are known as La Niña). El Niño/La Niña events have a strong impact on the weather locally, but also influence global weather patterns. The term Southern Oscillation refers to changes in the tropical atmosphere which tend to accompany El Niño/La Niña events.

Specialised El Niño/La Niña forecast products are provided for our users. See:

Many other potential sources of predictability are also represented in the forecast system.