Page History

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• 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-M-climate).

Confidence

On extended range web charts the confidence is "over-stated", because reliability diagrams consistently show that forecasts are over-confident.  Thus where a high probability of a particular type of event is predicted, the "true" chances of that event happening are actually less than the probability that is shown. 

Some broad indications of ensemble performance and predictability in the extended range should be taken into account when considering the extended range output.  Users are strongly encouraged to consult verification information - e.g. monthly forecast reliability diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure) or monthly forecast relative operating characteristics (ROC) diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure).  An explanation of reliability diagrams and ROC diagrams is given in the annex to this guide).  Users can also reference metrics that describe how skill tends to vary in different scenarios - see General use of Extended Range Output section.

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-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-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.

Circulation patterns

A major goal of Extended 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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• Whether the circulation applies to the whole region or whether a different flow is likely near the edge(s).  Confident winter-time forecast circulation can have a large spread in forecasts of 2m temperature due to atmospheric thermal gradients shifted away from their climatological positions.  
• Atmospheric dynamical processes (Rossby wave propagations, weather regimes, etc).
• Land Surface conditions: Snow cover, Soil moisture.
• Ocean conditions: Sea-surface temperature, Sea ice.
• Stratospheric initial conditions.
• Teleconnections, particularly those resulting from the Madden-Julian oscillation (MJO), have a significant impact on the forecast skill scores.

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Confidence

The extended range products should always be used with historical skill metrics in mind, as provided by verification probabilistic scores from the re-forecasts.

On extended range web charts the confidence is "over-stated", because reliability diagrams consistently show that forecasts are over-confident.  Thus where a high probability of a particular type of event is predicted, the "true" chances of that event happening are actually less than the probability that is shown. 

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-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-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 shadesSome broad indications of ensemble performance and predictability in the extended range should be taken into account when considering the extended range output.  Users are strongly encouraged to consult verification information - e.g. monthly forecast reliability diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure) or monthly forecast relative operating characteristics (ROC) diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure).

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

An explanation of reliability diagrams and ROC diagrams is given in the annex to this guide).  Users can also reference metrics that describe how skill tends to vary in different scenarios - see General use of Extended Range Output section..

Verification

The extended range products should always be used with historical skill metrics in mind.

Some broad indications of ensemble performance and predictability in the extended range should be taken into account when considering the extended range output.  Users are strongly encouraged to consult verification information:

• monthly forecast reliability diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure)
• monthly forecast relative operating characteristics (ROC) diagrams (for 2m temperature, surface temperature, total precipitation, mean sea level pressure).

An explanation of reliability diagrams and ROC diagrams is given in the annex to this guide).