Page History

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• For the medium range ensemble forecast system:
  • the horizontal resolution is increased to 9 Km
  • the vertical resolution remains unchanged at 137 model levels. 
  • the number of ensemble members remains unchanged at 50 members plus a control member.
  • the horizontal and vertical resolutions are identical to those of the High Resolution (HRES) in earlier versions of IFS.
  • the medium range ensembles are run twice daily from Day0-Day10 and slightly later from Day-0 to Day15.  
• For the extended range ensemble forecast system:
  • the horizontal resolution remains unchanged at 36 km.
  • the vertical resolution is increased to 137 model levels.  This is the same vertical resolution as the medium range ensemble ( and the High Resolution (HRES) in earlier versions of IFS)model.
  • the number of ensemble members is 100 members plus a control member.
  • the extended range ensemble is run daily from Day0-Day46.
• A multi-layer snow scheme was introduced.

Note: The extended range forecasts are not just an extension of the medium-range forecasts but are completely separate forecast systems.  However, both start from very similar analyses.  There are two sets of re-forecasts, one for the medium range and one for the extended range. 

The HRES and unperturbed (control) ensemble member of the medium range ensemble (CTRL):

• have the same horizontal and vertical resolution.
• are meteorologically equivalent.
• are equally skilful on average.  

However, they can diverge on a day-to-day basis due to small technical differences and also the chaotic nature of the atmosphere.  Nevertheless and are virtually identical.   Nevertheless the HRES will continue for the time being for ease of use by customers and users.

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