Through this designation process, GPCLRFs adhere to certain well-defined standards, aiding the consistency and usability of:
- fixed forecast production cycles
- standard sets of forecast products
- WMO-defined verification standards (for retrospective forecasts).
A comprehensive set of standard verification measures has also been defined, and is known as the WMO Standard Verification System for Long-Range Forecasts (SVSLRF).
At minimum, the following are required from GPCLRFs:
- Predictions for averages, accumulations, or frequencies over 1-month periods or longer (typically anomalies in 3-month-averaged quantities is the standard format for seasonal forecasts, and forecasts are usually expressed probabilistically)
- Lead time: between 0 and 4 months
- Issue frequency: monthly or at least quarterly
- Delivery: graphical images on GPCLRF website and/or digital data for download
- Variables: 2m temperature, precipitation, Sea Surface Temperature (SST), Mean Sea-Level Pressure (MSLP), 500hPa height, 850hPa temperature
- Long-term forecast skill assessments, using measures defined by the SVSLRF.