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Table of Contents

Creation of ER-M-Climate

The ER-M-Climate is derived from a set of sub-seasonal range re-forecasts created using the same calendar start dates over several years for data times either side of the time of the sub-seasonal ensemble run itself.  The re-forecast runs are at the same resolution as the sub-seasonal medium range run itself and run over the 46-day sub-seasonal range ENS period. 

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• sub-seasonal range forecast verification metrics are based on the re-forecasts.
  
• re-forecasts allow computation of the ER-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) mean that some calibration for model bias and drift into the products is incorporated.

Selection of sub-seasonal range re-forecasts

The set of re-forecasts is made up from:

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• to present the day15 to day46 ensemble meteograms with the sub-seasonal range climate (ER-M-climate).
• to highlight significant anomalies of forecast 2m temperature, wind speed, cloudiness and precipitation from the norm for a given location and time of year.  

Different reference periods for M-Climate and ER-M-Climate

ECMWF uses different reference periods but essentially the same re-forecast runs to build the M-Climate and the ER-M-Climate.   The key difference is that those runs are grouped and used in different ways:  

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Note before Cy41r1 in spring 2015, the M-climate was constructed from only 500 re-forecasts was more prone to sampling errors and as a result.

(FUG Associated with Cy49r1)