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 Fig8.1.4.2.6: A schematic illustration of the CDF (left) and PDF (right) for forecasts of 12hr accumulated precipitation showing the ENS T+48hr forecast (light green),  ENS T+96hr forecast (dark green) and ENS T+144hr (blue), together with the M-climate (black) verifying at the same time in the future.  The CDFs and PDFs both give, in different ways, a visual indication of mean, spread and asymmetry.

In Fig 8.1.4.2.6 the area between the CDF lines and M-climate, and hence the EFI, is becoming greater as the verifying time approaches.  This suggests increasing probability of an unusual rainfall event.  EFI approaches +1 on the T+48 forecast suggesting very unusual rainfall compared to climatology.  The steepness of the CDF and hence the peaked shape of the PDF charts at T+48 indicate that many of the ENS members are showing similar results and thus an extreme event of the magnitude indicated (on the x-axis) can be considered quite likely (assuming of course that the forecasts are not systematically biased).

Fig8.1.4.2.7: Schematic set of idealised CDFs from a series of ENS runs (cyan earliest, red latest), for a variable for which the climatological distribution is approximately Gaussian (e.g. 2m temperature).  If the M-Climate (or forecast) CDF curve resembles a "skewed S-shape" then that distribution is approximately Gaussian. 

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