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The Weekly Mean Anomaly charts show 7-day mean anomalies from the sub-seasonal climate of several forecast parameters.  Currently the forecast parameters are 2m air temperature, surface temperature, precipitation and mean sea level pressure.  The background colour shading in FigFig8.2.9.3 shows the anomaly of the forecast median from the mean of the model sub-seasonal climate (SUBS-M-climate).  These are shown in units of the variable displayed.  

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The relative spread is represented as the ratio of the ensemble forecast inter-decile range divided by the model climate inter-decile range (Fig1Fig8.2.9.1). 

Figure Fig8.2.9.1: Definition of terms used in deriving a quantile based product.  The diagram shows a schematic extract from a meteogram for "Weekly Mean Anomaly of precipitation from Subs-M-climate".  Letters denote:

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It is important to note, however, that all members of an ensemble are equally probable and no result should be discarded out of hand.

Figure2Fig8.2.9.2(A,B,C): Six Three examples of the distribution of sub-seasonal ensemble members compared with the sub-seasonal model climate. The shaded colours show range and probabilities of anomalies from the mean in the sub-seasonal model climate.  The  box and whisker plots show the range and probabilities of anomalies of the sub-seasonal ensemble members from their median.  Cumulative distribution functions are shown to help visualisation.  If the spread of the ensemble forecast is:

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It is important to note, however, that all members of an ensemble are equally probable and no result should be discarded out of hand.

Examples and usage

Figure3 Fig8.2.9.3 shows a forecast chart for mean 2m temperature for a period about 3 weeks into the future.In the figure:

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Purple contours (denoting a forecast spread larger than the climatological spread) are relatively uncommon.  When present the user should be particularly cautious and be careful not to over-interpret a forecast.  Purple contours can appear, for example, as a result of climate-change-related shifts in the cryosphere, or with forecasts of very wet conditions or with a case of severe drought. 

Figure3: Fig8.2.9.3: A forecast chart for mean 2m temperature for a period about 3 weeks into the future. 

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