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Sub-seasonal range forecasts

The sub-seasonal range forecasts provide a range of possible future weather states in an extended range.  It bridges the gap between medium-range and seasonal forecasting. 

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The medium range and sub-seasonal range models have the same structure and physics etc. but different spacial (but not vertical) resolutions and differing land-sea masks and orography.  Users should be aware that the output is effectively from different models.  The sub-seasonal range forecasts are not just an extension of the medium-range forecasts but are completely separate systems each starting from their own analyses.  There are two sets of re-forecasts, one for the medium range and one for the sub-seasonal range.  This is especially important if a time-series crosses the boundary between the end of the ensemble 15 day forecast and the start of the sub-seasonal range.  Users need to develop interpolation procedures that take these changes into account.

Sub-seasonal range products

The sub-seasonal range output is available on the ECMWF web charts and ecCharts. Guidance on the  Interpretation of the sub-seasonal range products is discussed elsewhere in the guide.

Specialised products

Specialised products for the sub-seasonal range include information on potential tropical cyclone activity and evolution of the Madden-Julian Oscillation (MJO).   The MJO is characterized by an eastward propagation of an area of more organised convection in the tropics, typically initiated over the Indian Ocean.  It is important as it can influence developments elsewhere on the globe:

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 The MJO has an influence on the forecast skill over the extra-tropics and MJO predictions are skilful well beyond Day20.  Typically the forecast reliability is enhanced when an MJO event is detected in the forecast initial conditions.

Additional sources of information

(Note: In older material there may be references to issues that have subsequently been addressed)

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