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The anomaly, as shown on some of the sub-seasonal range ensemble products, is the difference between the ensemble weekly mean of the real-time forecast and the corresponding ensemble weekly mean of the ERSUBS-M-climate.  On web charts, the regions where the significance of this anomaly (difference) is:

• greater than 99% are delimited by a dashed contour (blue: wetter, colder or lower pressure; red: drier, warmer or higher pressure).
• greater than 90% are coloured (blue: wetter, colder or lower pressure; red: drier, warmer or higher pressure).
• less than 90% are left blank (taken as not significantly different from ER SUBS-M-climate).

Circulation patterns

A major goal of sub-seasonal range forecasting is prediction, well in advance, of persistent, anomalous large scale circulation patterns that themselves can lead to severe weather events:

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A particular consideration when using the precipitation charts is that the range of colours available for "below average" anomalies (red colours) is constrained by the local climatology in the ER SUBS-M-climate.  For example if all ensemble members showed a dry week, the mean (-ve) anomaly could be no larger in magnitude than the mean in the ER SUBS-M-climate.  So in some locations the strongest dry signal one can ever see will only be in the first or the second of the red shades.

Anomaly charts (500hPa N Hem anomaly and Global and Regional anomaly) show how sub-seasonal range forecasts performed in the recent past in the lead up to a particular week.  The anomaly of one week of forecasts (relative to the ER SUBS-M-climate) is compared with the weekly mean anomalies (relative to the ER SUBS-M-climate) of recent sub-seasonal range forecasts verifying over the same period.   They give information about the consistency between the monthly forecasts from one week to another.

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