231: Target Season
If the Y input file consists of monthly data, CPT will prompt for the season to be forecast if it is unable to determine the season from information in the X file (specifically, the cpt:S and cpt:T flags need to be set, or the Options ~ Data ~ Synchronous Predictors flag must be switched on). The target season window will open automatically when both files have been opened, but the season options can be reset subsequently by selecting the Target Season menu item. There are three prompts:
- First month of season to forecast : the number of the first month of the target season (for example 2 for FMA);
- Length of season to forecast : the number of month in the target season (for example 3 for FMA);
- Total length of season including persistence component : the length of the target season plus the length of the season of recently observed values (for example 6 for a Nov - Apr season for which a forecast is made only for FMA).
Typically, the last value (for the total length of the season) would be the same as the second prompt (for the length of the target season). However, most frequently when making SPI predictions, a 3-month rainfall forecast may be added to 3 months of recently observed rainfall to obtain a predicted 6-month SPI. Alternatively, the annual average temperature could be predicted in early December by predicting the December temperature and combining this value with the observed 11-month average through November, in which cases the second and third prompts should be 1 and 11, respectively.
The value for the total length must be greater than or equal to the length of the season to forecast. If it is greater, then a persistence component will be included in the forecast, and the corresponding observations must be available in the Y file. If the Y observations are unavailable, a forecast cannot be made even in the X data are available.