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Table of Contents

Creation of M-Climate

The M-Climate is derived from a set of medium range re-forecasts.  These are created using the same calendar start dates over several years for data times either side of the time of the medium range ensemble run itself.  The re-forecast runs are at the same resolution as the medium range ensemble (currently 9km) and run over the 15-day medium range ensemble period.   

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  • medium range forecast verification metrics are based on the re-forecasts
  • re-forecasts allow computation of the M-climate.

Selection of medium range re-forecasts

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.

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  • to compare the meteograms from the 15-day ensemble forecast against the medium range climate (M-climate).
  • to deliver the extreme forecast index (EFI) and shift of tails (SOT) 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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  • Day1 M-climate is used with T+12h to 36h forecasts from the 12UTC run and T+0h to 24h forecasts from the 00UTC run.
  • Day2 M-climate is used with T+36h to 60h forecasts from the 12UTC run and T+24h to 48h forecasts from the 00UTC run.

Updates to M-climate

In Cy49 (introduced in autumn 2024) and later, re-forecasts are made every four days during each month on 1/5/9/13/17/21/25/29 (excluding 29 February).  There remain problems using each newly updated M-climate, particularly in spring and autumn when mean temperatures change most rapidly day by day. 

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Cy41r1 (introduced in spring 2015), the M-climate was constructed from only 500 re-forecasts was more prone to sampling errors and as a result.

Different priorities for M-Climate and SUBS-M-Climate

ECMWF uses different reference periods but essentially the same re-forecast runs to build the M-Climate and the SUBS-M-Climate.   The key difference is that those runs are grouped and used in different ways:  

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