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The weekly anomaly probability charts display the probability that the weekly mean anomalies are greater than zero.  The probability is calculated from the number of ensemble members which show an anomaly within the higher half of the the ER-M-climate distribution. 

Charts available are: 2m temperature, surface temperature, total precipitation, mean sea level pressure. 

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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). 

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• the proportion of members above the ER-M-climate mean is between 40% and 60%,
• or that that proportion, whatever it is, is not statistically significant.

This plot structure circumvents the fact that some ER-M-Climate distributions will be skewed (i.e. the climatological probability of seeing more than the mean is far from 50%).

Note: On precipitation charts the range of colours available for "below average" anomalies (brown colours) is constrained by the local climatology in the ER-M-climate.  For example if all ENS members showed a dry week, the mean (-ve) anomaly could be no larger in magnitude than the mean in the ER-M-climate.  So in some locations the strongest dry signal one can ever see will only be in the first or the second of the brown shades.

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The weekly anomaly probability charts display the probability that the weekly mean anomalies are in the lower or uppermost third (tercile), fifth (quintile) or tenth (decile) of the ER-M-climate distribution.

Charts available are: 2m temperature, surface temperature, total precipitation, mean sea level pressure.

The probability is calculated from the number of ensemble members which show an anomaly within the highest or lowest tercile, quintile or decile of the the ER-M-climate.

Terciles:  Three equally probable domains can be defined: below normal, normal and above normal.

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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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