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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.

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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.

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• 500hPa geopotential height.
• anomaly of 2m temperature.
• anomaly of 10m wind.
• anomaly of sunshine duration; the fraction of time there is sunshine compared with mean sunshine duration in the ER-M-climate (e.g. +0.01 means 1% more sunshine than in the ER-M-climate; -0.05 means 5% less sunshine).

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The northern mid-latitude Hovmöller diagrams show the time evolution of the ensemble mean anomaly of geopotential height at 500hPa or 1000hPa, averaged over the latitude band 35N-60N (Northern Extratropics) or 25S-50S (Southern Extratropics).  The anomaly has been computed by averaging all the members of the real-time forecast and subtracting the mean of the ER-M-climate.   Contours are plotted every 1.5dam.  Since it is an ensemble mean, the structures shown below the horizontal line are much more detailed in the first days of the forecast (top part) than in the last days (bottom part).   Shaded areas represent the ensemble spread and are displayed only when the amplitude of the anomaly exceeds 2dam.  On average spread will naturally increase with forecast lead time, though occasionally, when moving to longer lead times, there can be a reduction.

The Madden-Julian Oscillation (MJO) Hovmöller diagrams show the ensemble mean anomalies of outgoing long wave radiation, zonal wind at 850hPa, and velocity potential at 200hPa averaged over a tropical band (15N-15S). 

Tropical Storm Probabilities - Extended range forecast

These charts show the evolution of existing and potential tropical cyclone activity.

• Strike probability is the probability (in %) that a tropical cyclone will pass within a 300 km radius from a given location and within the 7-day time window.   The charts are based on the number of extended range ensemble members that predict a tropical cyclone, each member having equal weight. 
• Probability anomaly charts show whether the strike probabilities are higher (red shading) or lower (blue shading) than probabilities within a 20-year model climatology within the same 7-day time window.  They are computed by subtracting the model climatological probabilities from the real-time forecast probabilities.  Mean anomalies of probability are shown by the scale.
• Model extended range climate charts (ER-M-climate) show weekly mean strike probabilities (in %) within the same 7-day time window.

Tropical Storm Frequency - Extended range forecast

These charts show: 

• Tropical storm weekly mean frequency.  The frequency is derived by comparing the ensemble members probability with that of the 20-year model climatology probabilities within the same 7-day time window.
• Tropical storm weekly mean accumulated cyclone energy (ACE).  This is calculated by summing the square of the estimated maximum sustained velocity of every active tropical storm at six-hour intervals.  The ACE of a time period is the sum of the ACEs for each storm and takes into account the number, strength, and duration of all the tropical storms within the 7-day time window.

Large scale mean flow - Weekly mean anomalies 500hPa and 10hPa  - Extended range forecast 

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