Sub-seasonal range graphical output

Sub-seasonal range products are available on ecCharts:

All charts correspond to weekly means.

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• Extreme Forecast Index (EFI) and Shift of Tails (SOT):
  • Temperature at 2m 
  • Total precipitation

Sub-seasonal range products are available on web open charts (ecCharts):

All charts correspond to weekly means.

Weekly mean anomaly from model climate.

The weekly mean anomaly charts display the anomaly between the forecast weekly mean and the corresponding weekly mean in the ER-M-climate.

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In both cases in this example there is white shading on the maps at location X. The example shows white shading on the maps cannot, of itself, point to a forecast of average (as at week 1) nor to a 'don't know' forecast of climatology (as at week 5).

Probability that weekly mean anomaly from model climate greater than zero

The weekly anomaly probability charts display the probability that the weekly mean anomalies are greater than zero.  The probability is calculated from the number of ensemble members which show an anomaly within the higher half of the the ER-M-climate distribution. 

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Click on the central small icon in the bottom right of the web frame to show the colour scale of values appropriate to each display.

Probability of weekly mean anomaly from model climate (in terciles, quintiles, deciles)

The weekly anomaly probability charts display the probability that the weekly mean anomalies are in the lower or uppermost third (tercile), fifth (quintile) or tenth (decile) of the ER-M-climate distribution.

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Any pixel that has high probability for lower (or upper) decile should have at least the same or higher probability for lower (upper) quintile and even higher for lower (upper) tercile.  On occasion this has not happened and is being investigated.

Multiparameter outlook - sub-seasonal range forecast

These multi-parameter charts charts display the ensemble weekly mean:

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Click on the central small icon in the bottom right of the web frame to show the colour scale of values appropriate to each display.

Hovmöller diagram or Time-Longitudes diagram - sub-seasonal range forecast 

Hovmöller or Time-Longitudes diagrams show the time evolution of the ensemble mean anomaly of a parameter.  The x-axis represents the longitude, the y-axis represents the time evolution (time increasing downwards).  Past results lie above the horizontal line and forecast results lie below.  

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The Madden-Julian Oscillation (MJO) Hovmöller diagrams show the ensemble mean anomalies of outgoing long wave radiation, zonal wind at 850hPa, and velocity potential at 200hPa averaged over a tropical band (15N-15S). 

Large scale mean flow - Weekly mean anomalies 500hPa and 10hPa

The mean flow and anomaly charts show, at global or regional scales, the weekly:

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Any pixel that has high probability for lower (or upper) decile should have at least the same or higher probability for lower (upper) quintile and even higher for the tercile. 

Measures of skill of forecasts. 

The sub-seasonal range products should always be used with historical skill metrics in mind.

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• 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).

Relative Operating Characteristics diagrams

The Relative Operating Characteristics give a measure of the effectiveness of a forecast system to predict an event that actually happens balanced against forecast of an event that fails to occur.   ROC is derived from measuring the area beneath the results plotted on a ROC diagram.  ROC area values indicate:

• ROC value 1.0 implies consistent Hit Rate and no False Alarms.
• ROC value 0.5 implies no skill with as many Hits as False Alarms. 
• ROC value 0.0 implies consistent False Alarm rate and no Hits.

Reliability diagrams

The Reliability diagrams give a measure of the tendency of the forecast system to over- or under-forecast and event.  The diagram plots the frequency of a forecast probability of an event against the frequency that the event occurs.   Ideally these should match and is shown by the diagonal line. Where the plot lies:

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

ROCmap - map of Relative Operating Characteristics (ROC)

The ROCmap shows the ROC score computed over each grid point with a resolution of 2.5 degrees longitude by 2.5 degrees latitude.  The charts are anomalies derived from previous sub-seasonal range ensemble forecasts compared with ER-M-climate. 

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• Red: ROC > 0.5 - the monthly forecast has more skill than climatology (pink, reds, dark browns).
• Blue: ROC < 0.5 - the monthly forecast has less skill than climatology (cyan, blues, dark blues).

Ranked Probability Skill Score (RPSS) chart  

The RPSS map shows the RPSS score computed over each grid point with a resolution of 2.5 degrees longitude by 2.5 degrees latitude.

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• RPSS = 1 the forecast has perfect skill compared to the reference (assumed to be climatology) - the forecast is beneficial;
• RPSS = 0 the forecast has no skill compared to the reference - the forecast has no benefit over climatology;
• RPSS = a negative value the forecast is less accurate than the reference  - the forecast is misleading.

(FUG Associated with Cy49r1)