Forecast Probabilities

A set of three maps (if the data are gridded or station) or bar charts (otherwise) are shown. Each map indicates the forecast probability 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 probabilities are derived from the best-guess forecast (the regression estimate from the CCA, PCR, or MLR model) by assuming that the errors in the best-guess forecast will be normally distributed (or, more strictly, will follow a Student's t distribution), with the variance of the errors defined by the variance of the errors in the cross-validated predictions (alternative error variances can be set using Options ~ Forecast Settings ). If the Y data have been transformed it is assumed that the forecast errors of the transformed data will be normally distributed. From the best-guess forecast and the assumed error variance and distribution the probabilities of exceeding the various thresholds can be calculated.

The map titles can be reset using the Customise option upon right-clicking in the child window. Similarly the Customise ~ Contour Limits option provides some flexibility to adjust the scaling on the colour bars. A window opens that indicates the assumed maximum and minimum probabilities when setting the scaling and number of colours. These values can be reset, which will in turn automatically reset the colour intervals and number of colours. Greater flexibility for setting the colour levels is planned for future releases. Further options for customising the maps, including masking lakes or land areas, resetting the size of the fonts and of the image itself, are available from Options ~ Graphics .

The maps 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 probabilities can be saved from the Forecasts tab in File ~ Output Results .