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However, the final forecast in the sequence, DT 00UTC 09 May, used an updated M-climate as the basis for EFI and SOT computation.  So on the last two M-climate frames, the M-climate based on 4 May is replaced by that based on 8 May. This can be seen by the dark green boundary receding significantly to the north because the new M-Climate's focus is slightly later (and warmer) in the year.  This means that if the ENS forecast of 2m temp stays the same it will once again appear more extreme and this is shown with a return to a larger negative EFI value.

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Fig5.3.5-1: The frame on the left shows a sequence of extreme forecast index (EFI) and shift of tails (SOT) charts.  These are from ensemble forecasts at 12hr intervals with data times from 00UTC 05 May to 00UTC 09 May 2017.  All verify for the same 24hr period 00UTC 09 May to 00UTC 10 May 2017.  Large negative EFI values (Dark Blue, Purple) give strong indication of a significantly cold event compared with corresponding M-climate climatology (shown in the frame on the right).  However, the large negative EFI values (Purple) from forecasts several days previously gradually become less extreme and less extensive (Dark Blues). Then return to large negative EFI values (Purple) on the last forecast.  This is because M-climate has been recalculated reflecting the progressively warmer springtime temperatures experienced in the past.  The forecast temperatures, though not significantly lower than previous forecasts, now appear significantly lower and more extreme compared with the latest M-climate. 

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Fig5.3.5-2: The frame on the left shows Cumulative Density Function (CDF) of ensemble forecasts for northern Poland.  These are from ensemble forecasts at 12hr intervals with data times from 00UTC 05 May to 00UTC 09 May 2017.  All verify for the same 24hr period 00UTC 09 May to 00UTC 10 May 2017.  Each ensemble forecast has an associated colour. 

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