456: Odds Forecast

A set of three maps (if the Y-data are gridded or station) or bar charts (otherwise) are shown. Each map indicates the forecast odds for the three categories. The maps are shaded from blue for low probabilities, to red for high probabilities. If more than one forecast is produced, the forecasts can be cycled using the up and down arrows, or typing in the year. The odds (or more specifically the Hong Kong odds) are calculated from the forecast probabilities as:

probability / (1 - probability)

Alternatively, the odds relative to the climatological odds can be shown by selecting relative odds using the Options ~ Forecast Options menu item. The relative odds are the forecast odds divided by the climatological odds. For equiprobable tercile-based forecasts the climatological odds are:

0.333 / (1 - 0.333) = 0.5

or "2 to 1 against". If the forecast probability is 50%, the forecast odds are

0.5/0.5 = 1.0,

(or "even odds") and so the relative odds are:

1.0 / 0.5 = 2.0,

indicating that the odds have doubled (from 0.5 to 1.0).

The map/graph title can be changed by right-clicking on the image and then selecting the Customise ~ Title option. There is some flexibility to adjust the colour scaling on the maps: the colour bar limits can be set by right-clicking on the image and then selecting the Customise ~ Contour Limits option, and/or the number of colours can be set by selecting the Customise ~ Number of Colours option. In the case of index data, the graph Y-axis limits can be set using the Customise ~ Axis Limits option, and the number of tick marks can be set using the Customise ~ Number of Tick Marks option. Further options for customising the graphics, including adjusting the size of the fonts, and the size of the images, plus masking of land or lake areas for the maps are available from Options ~ Graphics .

The images can be saved as graphics files, individually or as a montage, by right-clicking anywhere in the child window and selecting Export from the pop-up menu. A default name is given to the graphics file, but this name can be changed using the browse button. The image quality for all the graphics formats can be improved by increasing the size of the image (see Options ~ Graphics ~ Graph Scaling ).

The forecast odds or relative odds can be saved from the Forecasts tab in File ~ Output Results .