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Clustering

Clustering is the process where individual ensemble members that are "similar" according to some measure (or norm) are be grouped together.  This compresses the large amount of information produced by ensemble members and highlights the most predictable parts.  Clustering can be performed:

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• Weather scenario clustering is performed on medium range ensemble forecast output over a restricted area covering Europe and the northwest Atlantic.  It highlights the differences between medium range scenarios in terms of the large-scale flow.  
• Weather regime clustering summaries are based on one of four climatological regimes which have been derived from reanalysed data over an area covering Europe, eastern Canada, and the north Atlantic.  This is used beyond day10 of the medium range ensemble forecast output to provides information about the possible transitions between regimes.
• Weather regime clustering summaries are based on one of six climatological regimes which have been derived from reanalysed data over a slightly larger area covering Europe, eastern Canada, the North Pole region and the north Atlantic.  This is used with extended range and seasonal ensemble forecast output and provides information about the possible transitions between regimes.

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