For a statement of the motivation and requirements for this feature, see Confluence document Multiple climatological normal periods on the PCDS - Conceptual work plan. Summary:

• The last time that PCIC produced a set of 30-year climatologies (the 1971-2000 period) for PCDS station observations was 2012. At that time, the PCDS data portal was still in its infancy and there was no need to differentiate between various 30 year normal periods, because there was only one set of climate normals available.
• In order to make climatologies available via the PCDS data portal on short notice, all of the climatologies were added the to PCDS database, differentiated by only by using specially named variables, but intermixed with the "raw" recorded meteorological observations.
• With the advent of two new normal periods (1981-2010 and 1991-2020) and the associated sets of climatologies, it is required that the climatologies be properly separated from the raw observations and be tracked and attributed according to their climatological period.
• It is also required to improve the PCDS portal to make all climatology periods available and allow interested parties to select between them.
• Additionally, it is common practice, when creating climatologies to utilize information from multiple neighboring stations within a small area if available and pulling their records together to create a single "composite station".

Data modelling for this feature is found in Data model(s) for multiple climatological normal periods. This data modelling is now in a state suitable for an initial implementation and testing. In summary, it adds the following tables to the CRMP database:

• Climatological Station
• Climatological Station Histories (association table for Histories that contribute to the Climatological Station)
• Climatological Variable
• Climatological Value

There are some outstanding questions about this design, but none that prevent work from going forward on it.