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Re-forecasts are made every four days during each month on 1/5/9/13/17/21/25/29 (excluding 29 February).  These are the re-forecast base-dates for medium range.

The set of re-forecasts for forecasts for the M-climate s made up from:

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  • nine consecutive re-forecasts

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  • centred on the M-climate base date and covering a forecast period of 15 days

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  • .  The middle

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  • re-forecast corresponds to the

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  • closest base-date preceding the actual ensemble run date.

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  • re-forecasts are derived by re-

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  • running an 11-member ensemble (1 control and 10 perturbed members)

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  • using the same calendar start date for each of the last 20 years.  Thus there are 20 years x 9

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  • re-forecasts x 11 ensemble members = 1980 re-forecast values.

These are available at forecast intervals of 6 hours for each forecast parameter, for each forecast lead-time and for each calendar start date and location.  They are used to define the M-Climate.

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The M-climate is used in association with the ensemble forecast:

  • to present compare the meteograms from the 15-day ensemble meteograms with forecast against the medium range climate (M-climate).
  • to deliver the extreme forecast index (EFI) and shift of tails (SOT) products  products. 
  • to highlight significant forecast departures of 2m temperature, wind speed, cloudiness and precipitation and other parameters from the norm for a given location and time of year.  

 Values evaluated in M-climate

  • 2m temperature.
  • soil temperature.
  • sea-surface temperature.
  • mean sea level pressure.
  • precipitation.
  • cloudiness. 

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