Through this designation process, Global Producing Centres of Long-Range Forecasts adhere to certain well-defined standards, aiding the consistency and usability of:
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fixed forecast production cycles
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standard sets of forecast products
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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.
At minimum, the following are required from the Global Producing Centres:
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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)
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Lead time: between 0 and 4 months
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Issue frequency: monthly or at least quarterly
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Delivery: graphical images on GPC-LRF website and/or digital data for download
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Variables: 2 meters temperature, precipitation, Sea Surface Temperature (SST), Mean Sea-Level Pressure (MSLP), 500hPa height, 850hPa temperature
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Long-term forecast skill assessments, using measures defined by the WMO Standard Verification System for Long-Range Forecasts
