Page History

Creation of S-M-Climate

The S-M-Climate is derived from a set of seasonal re-forecasts are created using using the same calendar start dates for each of the last 20 years for the same data time of the seasonal run itself.  The re-forecast runs are at the same resolution as the seasonal run itself (currently 36km) and run over the 7 month or 13 month period of a seasonal forecast   

Seasonal re-forecasts for verification

There is some merit in examining the real-time performance of a seasonal forecasting system.  But the sample sizes created for one system are far too small to conclude anything about the true performance levels of that system. Hence we use the re-forecasts.  

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• seasonal forecast verification metrics are based on the re-forecasts
  
• re-forecasts allow computation of the S-M-climate which allows actual forecasts to be converted into an anomaly format.   Forecasts in terms of anomalies relative to a model climate (rather than relative to the observed climatology) means that some calibration for model bias and drift into the products is incorporated.

Selection of seasonal re-forecasts

The set of re-forecasts is based on using the same calendar start date (the 1st of each month) during a fixed period (36 years: Jan 1981 to Dec 2016).   Currently, this is not updated.

Each re-forecast consists of a 25-member ensemble (all members are perturbed) run over a 7-month forecast period for monthly runs, and a 13-month forecast period for quarterly runs.  Therefore altogether 36 years x 25 ENS members = 900 re-forecast values are available to define the S-M-climate for each forecast parameter, forecast lead-time, calendar start date (the 1st of each month) and location.  These are used in their entirety for skill and reliability assessment, and verification maps are accordingly provided on the web.

Seasonal re-forecasts for the S-M-climate

For actual forecast products the re-forecast period utilised is a subset of that used for verification.  

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