Section 2.1.2 Model Configurations

• Section 2.1.2.1 ENS - Ensemble Forecasts
• Section 2.1.2.2 ENS Extended-Range Forecast
• Section 2.1.2.3 ENS Long-Range (Seasonal) Forecast
• Section 2.1.2.4 HRES - High Resolution Forecasts

Model Configurations

The IFS models the dynamics of the atmosphere and the physical processes that occur, and also other processes that influence the weather e.g. atmospheric composition, surface energy fluxes, the marine environment and processes at the atmosphere/surface interface (then scroll down to soil/surface section).  Several configurations of the atmospheric model are used, each tailored towards a specific aim:

• HRES to investigate detail in the forecast during the first 10 days.
• Ensemble ENS to investigate detail and uncertainty in the forecast during the first 10days or 15days.
• Extended ENS and Seasonal runs to give probability of general conditions at longer ranges.

There are some slight differences, but generally the same model structure is used in each of the different model configurations.  The relative skill of the models and their strengths have been investigated.

Major changes introduced with Cy48r1 Spring 2023

Some major changes were made to the IFS with the introduction of the Cy48r1 in Spring 2023.

After the introduction of  Cy48r1 in Spring 2023 the:

• High Resolution (HRES):
  •  is run four times daily:
    • base times 00 UTC and 12 UTC, producing a 10 day forecast (T+0 to T+240).
    • base times 06UTC and 18UTC, producing a 3.75 day forecast (T+0 to T+90).
  • has horizontal resolution of 9 Km and vertical resolution of 137 model levels.
  • documentation gives details of HRES products and dissemination schedules.
• medium range ensemble (ENS):
  • is run four times daily:
    • base times 00 UTC and 12 UTC, producing a 10 day forecast (T+0 to T+240) and also a 15 day forecast (T+0 to T+360).
    • base times 06UTC and 18UTC, producing a 6 day forecast (T+0 to T+144). Results from these runs are:
      • used in Early cut off analysis (SCDA) and Long window data analysis (LWDA).
      • disseminated T+0 to T+72.
  • has horizontal resolution of 9 Km and vertical resolution of 137 model levels.  These values are the same as those of the High Resolution (HRES).
  • has 50 ensemble members plus an unperturbed control member (CTRL).
  • the unperturbed control member (CTRL) corresponds to the High Resolution (HRES) in earlier IFS versions.  CTRL forecasts maintain continuity of output for users.
  • documentation gives details of medium range products and dissemination schedules.
• extended range ensemble:
  • is run once daily, base time 00 UTC, producing a 46 day forecast (Day0 to Day46).
  • has horizontal resolution of 36 Km and vertical resolution of 137 model levels.  
  • has 100 members plus an unperturbed control member.
  • documentation gives details of extended range products and dissemination schedules.
• a multi-layer snow scheme was introduced.

The extended range forecasts are not just an extension of the medium-range forecasts but are completely separate systems both starting from their own analyses.  There are two sets of re-forecasts, one for the medium range and one for the extended range.

Before the introduction of Cy48r1 in Spring 2023 the: 

• High Resolution (HRES):
  • had horizontal resolution of 9 Km and vertical resolution of 137 model levels.
• medium range ensemble (ENS):
  • had horizontal resolution of 18 Km and vertical resolution of 137 model levels (higher horizontal resolution after Cy48r1).
  • had 50 ensemble members plus a control member.
  • the medium range ensemble was run twice daily from Day0-Day15.  
• extended range ensemble:
  • had horizontal resolution of 36 Km and vertical resolution of 91 model levels (higher vertical resolution after Cy48r1).  
  • had 50 members plus a control member (doubled the number of ensemble members after Cy48r1).
  • the extended range ensemble was run daily from Day0-Day46.
• a single-layer snow scheme was used.