This document proposes a set of best practices and guidelines for implementing and using the Open Geospatial Consortium (OGC) Web Map Service (WMS) to serve maps which are members of an ensemble of maps, each of which is a valid possible alternative for the same time and location. In the meteorological and oceanographic communities, it is Best Practice to produce a large number of simultaneous forecasts, whether for a short range of hours, a few days, seasonal or climatological predictions. These ensembles of forecasts indicate the probability distributions of specific outcomes. This document describes how to unambiguously specify an individual member of an ensemble, or one of a limited set of map products derived from a full ensemble.
In particular, clarifications and restrictions on the use of WMS are defined to allow unambiguous and safe interoperability between clients and servers, in the context of expert meteorological and oceanographic usage and non-expert usage in other communities. This Best Practice document applies specifically to WMS version 1.3, but many of the concepts and recommendations will be applicable to other versions of WMS or to other OGC services, such as the Web Coverage Service.