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Extended Range Output

The output is rather different from the shorter period output of HRES and ENS products.  It provides a more general overview of the forecast up to Day46, focusing mainly on the week-to-week changes in the weather rather than attempting to give unsupportable detail on individual days.  Output is mostly in the form of anomalies relative to ER-M-climate and is mainly shown as 7-day means for calendar weeks Monday-Sunday.   Specialised products for the extended range also include information on potential tropical cyclone activity and the MJO during the coming month.

Availability of Graphical Products

For each point of the chart the atmospheric variables (e.g. 2m temperature, surface temperature, total precipitation, mean sea level pressure) have been averaged over week-long periods.  Extended range 7-day mean forecast chart products are available to day 28 or 32 (depending on day of issue) on web charts, and to day 46 on ecCharts.  

Extended Range Runs

Anomaly Periods available on  web-charts

 Anomaly Periods  availability on ecCharts

Anomaly Periods Days

 Calendar Weeks (Mon-Sun)¤

Model Weeks for output (Days 1-7 etc)

Mondays:

days   1 to   7


days   8 to 14


days 15 to 21


days 22 to 28

days   1 to   7

days   5 to 11

days   8 to 14

days 12 to 18

days 15 to 21

days 19 to 25

days 22 to 28

days 26 to 32

days 29 to 35

days 33 to 39

days 36 to 42

days 40 to 46

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Week 1


Week 2


Week 3


Week 4


Week 5


Week 6

Week 1


Week 2


Week 3


Week 4


Week 5


Week 6

Thursdays:

days   5 to 11


days 12 to 18


days 19 to 25


days 26 to 32

days   1 to   7

days   5 to 11

days   8 to 14

days 12 to 18

days 15 to 21

days 19 to 25

days 22 to 28

days 26 to 32

days 29 to 35

days 33 to 39

days 36 to 42

days 40 to 46

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun

Thu - Wed

Mon - Sun


Week 2


Week 3


Week 4


Week 5


Week 6


Week 7

Week 1


Week 2


Week 3


Week 4


Week 5


Week 6

Table 1: Extended range forecast data: 7-day forecast periods available on web charts and ecCharts. Note: Website extended range forecast anomaly periods are aligned so that output from Monday and Thursday runs may be directly compared.

¤ Note, there is some ambiguity for Thursday forecasts regarding what should be labelled week 1 and what should be labelled week 2 (etc).

Correct use of charts - the difference between significance and confidence

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

  • greater than 99% are delimited by a solid 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% (taken as not significantly different from ER-M-climate) are left blank.

Note: Blank areas denote regions where the forecast distribution of outcomes, relative to the ER-M-Climate distribution of outcomes, is not significantly different at the 90% confidence level.  Overall, on extended range web charts, the confidence one can have in the forecast is "over-stated", because reliability diagrams consistently show that forecasts are over-confident. This means, for example, that if a high probability of a particular type of event is predicted, the "true" chances of that event happening are actually less than the probability shown. 

Some broad indications of ENS 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 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 ENS 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.

Updated/Amended 24/10/20 - amended chart links to open access.

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