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ENS - Ensemble Forecasts

The ensemble forecast suite (ENS) forecasts provide  provides a range of possible future weather states in the medium range.  This allows investigation of the detail and uncertainty in the forecast during the first 10days or 15days.

The ensemble forecast suite runs daily from base ensemble:

• is run twice daily, base times 00 UTC and 12 UTC

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• , producing a 10 day forecast (Day0 to Day10) and also a 15 day forecast (Day0 to Day15). 
• has horizontal resolution of 9

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• Km and vertical resolution of 137 model levels

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• .  These values are the same as those of the High Resolution (HRES) in IFS versions before Cy48r1).
• has land-atmosphere and ocean-atmosphere coupling.
• has 50 ensemble members plus a control member (control10 for the 10 day forecast, control15 for the 15 day forecast).
• control10 is the unperturbed ensemble member and corresponds to the High Resolution (HRES) in earlier IFS versions before Cy48r1.

The ensemble consists of .  The ensemble consists of one unperturbed member (the control) and 50 perturbed members that are similar to the control but their initial states and model physics have been perturbed to explore the currently understood range of uncertainty in the observations and the model.  A set of medium range re-forecasts provide a basis for the medium range model climate M-Climate.

The medium range ensemble 10 day forecast runs with data analysed from the short cut off analysis (SCDA).  Perturbations are derived.   ????? 

The medium range ensemble 15 day forecast runs with data analysed from the short cut off analysis (SCDA).  Perturbations are derived.   ????? 

When averaged over many forecasts each of the perturbed members has lower skill than the control (or, for that matter, HRES*), though control though any individual forecast might show a higher skill.  There is a range of products to present the information from the ensemble in different ways , and appropriate for different uses including .  These include probabilities, 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 ENS model climate (M-climate), such as meteograms and the Extreme Forecast Index and Shift of Tails (EFI/SOT).   From these one can infer, for example, whether conditions (temperature, rainfall, etc.) are likely to  The ENS products and chart presentations show where and when weather may deviate from the average for the location and time of year, and whether if such an anomaly could be extreme.  The ENS products and presentation in chart or diagram form are described later in the user guide.

ENS forecasts are run coupled to the Wave model (ECWAM) and the Dynamic Ocean model (NEMO) which includes modelling of sea ice (LIM2).  Atmosphere-ocean coupling occurs every hour.  This high-frequency coupling generally has a positive impact on the forecast development of synoptic-scale systems , such as tropical cyclones.The ENS runs are extended at lower resolution on Mondays and Thursdays from Day15 to Day46 based on 00UTC data time (the extended range forecasts(e.g. tropical cyclones).

Definitive information on the ECMWF dissemination schedule and products can be found in the the Catalogue of ECMWF real-time products (ENS: Set iii).

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