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Note that whilst negative SOT values can be computed, and are displayed in meteogram format (as above), and are illustrated below, we advise the user to generally focus on SOT values that are ≥0.8.

OpenChart display

Extreme Forecast Index (EFI) - Extended Range Forecast

These EFI charts aim to point to areas where unusually anomalous temperature or precipitation is likely to occur.

The EFI temperature chart shows the weekly mean EFI for 2 m temperatures.  This is derived from the distribution of ensemble forecast 2 m temperatures compared with the temperature distribution in the ER-M-climate.

The EFI precipitation chart shows the weekly mean EFI for precipitation.  This is derived from the distribution of ensemble forecast precipitation compared with the precipitation distribution in the ER-M-climate.

Click on the central small icon in the bottom right of the web frame to show the colour scale of values appropriate to each display.

Experience suggests :

• EFI values between 0.5 to 0.8 (irrespective of sign) can be generally regarded as signifying that “unusual” weather is likely,
• EFI values greater than 0.8 (irrespective of sign) usually signifies that “very unusual” or extreme weather is likely.

The SOT index provides information about how extreme an event could potentially be.  Positive SOT values indicate that at least 10% of the ensemble is forecasting an "extreme event" and a high value shows how extreme:

• Dashed black isopleths show SOT values associated with the 10% of ENS results (quantile 10) showing the coldest temperatures.
• Solid black isopleths show SOT values associated with the 10% of ENS results (quantile 90) showing the warmest temperatures or most precipitation.

Extended Range CDFs.

Cumulative Distribution Function (CDF)s for ensemble temperature and rainfall forecasts may be constructed from ensemble extended range forecasts.   It is important to note that here it is anomalies from the "norm" that are considered rather than absolute temperature or rainfall values.  The anomalies for the extended range climate (ER-M-climate) (black line) are the frequencies of departures from the mean (here defined as the "norm") of the ER-M-climate for the date in question (i.e.the light green lines on the diagram indicate the value at 50% probability and marked as 0°C anomaly).   Some anomalies are positive, some in the tails of the plot are extremely positive; some are negative, some some in the tails of the plot extremely negative.   The CDF for the ensemble values is constructed from the anomaly of the temperature forecast by each ensemble member (red line) as a departure from the mean or "norm" of the ER-M-climate.

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