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The ensemble median is is more suited to parameters like wind speeds and precipitation because these usually have skewed distributions.  

Ensemble spread and Standard Deviation

The ensemble spread is a measure of the difference of a forecast between the ensemble members.

The ensemble spread and is represented by the standard deviation (Std) with respect to the ensemble mean (EM).  Theoretically

Theoretically, on average, :

• small spread or low standard deviation indicates high forecast accuracy

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• large spread or high standard deviation indicates low forecast accuracy.     

The   The ensemble spread should reflect the diversity of all possible outcomes.  

The ensemble spread is flow-dependent and varies for different parameters.  It usually increases with the forecast range, but there can be cases when the spread is larger at shorter forecast lead times than at longer.  This might happen when the first days are characterized by strong synoptic systems with complex structures but are followed by large-scale fair weather high-pressure systems.

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