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Re-forecasts provide a Seasonal model climate (S-M-climate) against which to compare the actual forecasts.  The re-forecasts for a given system (now SEAS5) are all created before the System comes into operation.  In this sense the re-forecast strategy differs from the update-in-real-time approach used for shorter ranges (ER-M-climate and M-climate).  The distributions of the seasonal ensemble forecasts can be compared with the corresponding S-M-Climate distributions to give information regarding forecast anomalies.

Availability

Seasonal forecast output is available:

• at 12UTC on 5th of the months Jan, Mar, Apr, Jun, Jul, Sep, Oct, Dec for forecasts of months 1-7.
• at 12UTC on 5th of the months Feb, May, Aug, Nov for forecasts of months 1-13.

Forecast ranges & resolution

Graphical Products

For each point of the chart the atmospheric variables (e.g. 2m temperature, surface temperature, total precipitation, mean sea level pressure) are averaged values over month-long periods.  

Use of the Long-Range (Seasonal) Output

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

• More information on products available from the atmospheric model ensemble, long range forecast (Set V - SEAS) are available on the ECMNWF website.
• ECMWF SEAS5 User Guide
• ECMWF Seasonal Forecast Graphical Products (Forecast products and Verification measures).