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• The chart displays the probability of the forecast anomaly lying in the upper half of the ER-M-climate distribution (i.e. above normal; warmer or wetter etc than the mean of the ER-M-climate). 

White on the plot means that either:

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Multiparameter outlook - Extended range forecast

These multi-parameter charts charts display the ensemble weekly mean:

• 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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Hovmöller or Time-Longitudes diagrams show the time evolution of the ensemble mean anomaly of a parameter.  The x-axis represents the longitude, the y-axis represents the time evolution (time increasing downwards).  Past results lie above the horizontal line and forecast results lie below.  

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). 

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