Long range

Long range forecasts provide information about expected future atmospheric and oceanic conditions, averaged over periods of one to three months. Like the medium and extended ranges, the long range forecasts are produced by the IFS coupled ocean-atmosphere model. Long term predictions rely on aspects of Earth system variability which have long time scales (months to years) and are, to a certain extent, predictable. The most important of these is the ENSO (El Nino Southern Oscillation) cycle. Although ENSO is a coupled ocean-atmosphere phenomenon centred over the tropical Pacific the influence of its fluctuations extends around the world. Many other sources of predictability are also represented by the forecast system.

Long range forecasts are released every month and extend seven months in the future. Annual range forecasts are produced with the same system every three months, and extend thirteen months in the future.

Long and annual range forecast charts.

Upgrade to SEAS5

The fifth generation of the ECMWF seasonal forecasting system, SEAS5, was introduced 1 November 2017, replacing System 4. SEAS5 includes updated versions of the atmospheric (IFS) and interactive ocean (NEMO) models and adds the interactive sea ice model LIM2.

The table below summarizes the upgrades in model components and initialization for SEAS5.

  System 4 SEAS5
IFS Cycle 36r4 43r1
IFS horizontal resolution TL255 TCO319
IFS Gaussian grid N128 (80 km) O320 (35 km)
IFS vertical resolution (TOA) L91 (0.01 hPa) L91 (0.01 hPa)
IFS model stochastic physics 3-lev SPPT and SPBS 3-lev SPPT and SPBS
Ocean model

NEMO v3.3

NEMO v3.4

Ocean horizontal resolution ORCA 1.0 ORCA 0.25
Ocean vertical resolution L42 L75
Sea ice model Sampled climatology LIM2
Atmosphere initialization
ERA-Interim/Operations ERA-Interim/Operations

Land Initialization

ERA-Interim land (36r4)/Operations ERA-Interim land (43r1)/Operations
Ocean initialization ORA-S4 OCEAN5
Forecast ensemble size

51 (0-7m)

15 (8-13m)

51 (0-7m)

15 (8-13m)

Re-forecast years 30 (1981-2010) 36 (1981-2016)
Re-forecast ensemble size

15 (0-7m)

15 (8-13m)

25 (0-7m)

15 (8-13m)

Calibration period 1981-2010 1993-2016

SEAS5 documentation

         Please provide feedback on the SEAS5 user guide, so it can continue to be improved.

  • Articles describing and assessing SEAS5 are in preparation for submission to peer-reviewed literature
  • SEAS5 uses IFS cycle 43r1

EUROSIP multi-model system

The EUROSIP multi-model seasonal forecasting system consists of a number of independent coupled seasonal forecasting systems integrated into a common framework. From March 2017  the systems include those from ECMWF, the Met Office, Météo-France, NCEP and JMA.

For more information see the documentation of the EUROSIP system.

EUROSIP multi-model forecast charts

ECMWF Seasonal forecast system operational history

System 4

System 3

System 2

  • Operational from to January 2002 to February 2007
  • System 2 user guide

System 1

  • Produced forecasts from January 1997 to December 2001
  • System 1 user guide