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• • is run four times daily:
    • Day0 to Day15 based on 00UTC and 12UTC data and results are disseminated T+0 to T+360.
    • Day0 to Day6 based on 06UTC and 18UTC data and results are disseminated T+0 to T+72.
  • has horizontal resolution of 9 Km and vertical resolution of 137 model levels.
  • has land-atmosphere and ocean-atmosphere coupling.
  • has 50 ensemble members plus an unperturbed ensemble control member.
  • runs with data analysed from the Short Early cut off data analysis (SCDA).
  • the unperturbed Ensemble Control Forecast runs before the medium range ensemble starts.
  • results from the Ensemble Control Forecast runs are used in Early cut off analysis (SCDA) and Long window data analysis (LWDA).
  • dissemination schedule:
    • Ensemble control forecasts, schedules and products: Atmospheric model analysis and 15 day forecast of Ensemble Control Forecast (Sets I-i, I-ii, I-iii as shown for 00UTC and 12UTC base times).
    • Ensemble control forecasts, schedules and products: Atmospheric model analysis and 6 day forecast of Ensemble Control Forecast (Set I-i as shown for 06UTC and 18UTC base times). 
    • Medium range forecasts, schedules and products:  Atmospheric model analysis and 15 day forecast ensemble (Set III as shown for 00UTC and 12UTC base times).
    • Medium range forecasts, schedules and products: Atmospheric model analysis and 6 day forecast ensemble  (Set III as shown for 06UTC and 18UTC base times).  

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The ensemble members have identical model structure to the unperturbed control forecast member but differ only that initial states and model physics have been perturbed.  This allows exploration of the currently understood range of uncertainty in the observations and the model forecasts.   When averaged over many forecasts each of the perturbed members has lower skill than the unperturbed control member.  Nevertheless any individual forecast might show a higher skill.

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A range of ensemble products show information in different ways appropriate for different uses.  These include probabilities and clusters of alternative scenarios, and tropical cyclone and extra-tropical cyclone products.  Certain important products are based on, or directly show, anomalies relative to the M-climate.  Particularly important are meteograms and the Extreme Forecast Index and Shift of Tails (EFI/SOT).   The ENS products and chart presentations show where and when weather may deviate from the average for the location and time of year, and if such an anomaly could be extreme.

Ensemble forecasts are run coupled to the Wave model (ECWAM), and the Dynamic Ocean model (NEMO) which includes modelling of sea-ice (SI3).  Atmosphere-ocean coupling occurs every hour.  This high-frequency coupling generally has a positive impact on the forecast development of synoptic-scale systems (e.g. tropical cyclones).

The current medium range ensemble, including the control, has horizontal resolution of ~9km and a vertical resolution in 137 levels.  The high horizontal and vertical resolutions have the benefit of feeding energy from smaller to larger scale features (as happens in the real atmosphere).  But also risks developing or amplifying spurious small features, or suppressing existing ones that should be retained.  

A set of medium range re-forecasts provide a basis for the medium range model climate (M-Climate).

See a comprehensive description of medium range forecast output and medium range ensemble forecast output.  Some are additional products that are only available by arrangement.

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• View the ECMWF outline information on the rational behind probabilistic weather forecasts.
• View the ECMWF eLearning module on the Ensemble Forecasting Introduction - Sources of Forecast Uncertainty.
• read more on medium range forecasting.

(FUG Associated associated with Cy50r1)

Links OK, Read OK, Diags OK.

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