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For systems with lagged ensembles having multiple start dates, the "nominal" start date is assigned as follows:

Météo-France (all systems):

• Forecasts/Hindcasts: nominal month M includes the members initialised in the last weeks of month M-1 and on the 1st of month M

NOTE: Even though the different members of all Météo-France forecasting system ensembles are initialized using a lagged approach, the real start dates are not revealed to the users, so all members are encoded as if they were initialized on the 1st of the month

GloSea5-GC2:

• Forecasts: nominal month M includes the members initialised on the 1st of month M and all available members with start dates back to, and including, the 2nd of month M-1
  • Note that even though just the most recent 50 members are used for C3S products, the complete set of members are available through the CDS
• Hindcasts: nominal month M includes the members initialised on the 1st of month M and on the 25th, 17th and 9th of month M-1

NCEP:

• Forecasts: nominal month M includes the members initialised on the 1st of month M and all available members with start dates back to, and including, the 2nd of month M-1
  NCEP:
  • • Note that even though just the most recent 52 members are used for C3S products, the complete set of members are available through the CDS
  • Hindcasts: nominal month M includes the members initialised on the 1st of month M (if available) and on all start days from month M-1 except the 1st (see table below)Forecasts: nominal month M includes the members initialised on the 1st of month M and all available members with start dates back to, and including, the 2nd of month M-1

  Nominal start month	Dates used for C3S products	Additionally available dates
  JANUARY	1 January; 27, 22 and 17 December	12, 7 and 2 December
  FEBRUARY	31, 26, 21 and 16 January	11 and 6 January
  MARCH	25, 20, 15 and 10 February	5 February
  APRIL	1 April; 27, 22 and 17 March	12, 7 and 2 March
  MAY	1 May; 26, 21 and 16 April	11 and 6 April
  JUNE	31, 26, 21 and 16 May	11 and 6 May
  JULY	30, 25, 20 and 15 June	10 and 5 June
  AUGUST	30, 25, 20 and 15 July	10 and 5 July
  SEPTEMBER	29, 24, 19 and 14 August	9 and 4 August
  OCTOBER	28, 23, 18 and 13 September	8 and 3 September
  NOVEMBER	28, 23, 18 and 13 October	8 and 3 October
  DECEMBER	27, 22, 17 and 12 November	7 and 2 November