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Building a Numerical
Weather Prediction System

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(Last updated 14 June 2002)


The main purpose of the Global Data-processing System (GDPS) shall be to prepare and make available to Members in the most cost-effective way meteorological analyses and forecast products. The design, functions, organizational structure and operations of the GDPS shall be in accordance with Members' needs and their ability to contribute to and benefit from the system.


2.1    The real-time functions of the GDPS shall include:

(a)    Pre-processing of data, e.g. retrieval, quality control, decoding, sorting of data stored in a database for use in preparing output products;

(b)    Preparation of analyses of the three-dimensional structure of the atmosphere with up-to-global coverage;

(c)    Preparation of forecast products (fields of basic and derived atmospheric parameters) with up-to-global coverage for one to 10 days ahead;

(d)     Preparation of specialized products such as limited area very fine-mesh short-, medium-, extended-, and long-range forecasts, tailored products for marine, aviation, environmental quality monitoring, and other purposes;

(e)    Monitoring of observational data quality.

(f)    Post-processing of NWP data using workstation and PC based systems with a view to producing tailored value added products and generation of weather and climate forecasts directly from model output.

2.2    The non-real-time functions of the GDPS shall include:

(a)     Preparation of special products for climate-related diagnosis (i.e. 10-day or 30-day means, summaries, frequencies and anomalies) on a global or regional scale;

(b)    Intercomparison of analysis and forecast products, monitoring of observational data quality, verification of the accuracy of prepared forecast fields, diagnostic studies and NWP model development;

(c)     Long-term storage of GOS data and GDPS products, as well as verification results for operational and research use;

(d)    Maintenance of a continuously updated catalogue of data and products stored in the system;

(e)     Exchange between GDPS centres of ad hoc information via distributed data bases;

(f)    Conduct of workshops and seminars on the preparation and use of GDPS output products.


The GDPS shall be organized as a three-level system of World Meteorological Centres (WMCs),Regional Specialized Meteorological Centres (RSMCs) and National Meteorological Centres (NMCs), which carry out GDPS functions at the global, regional and national levels, respectively. The GDPS shall also support other WMO Programmes and relevant programmes of other international organizations in accordance with policy decisions of the Organization.


4.1     The general functions of GDPS centres shall be as follows:

4.1.1     World Meteorological Centres (WMCs)

These shall consist of centres applying sophisticated high-resolution global NWP models and preparing for distribution to Members and other GDPS centres the following products:

(a)     Global (hemispheric) analysis products;

(b)     Short-, medium-, extended- and long-range forecasts and products with a global coverage, but presented separately, if required, for:

(i)     The tropical belt;

(ii)     The middle and high latitudes or any other geographical area according to Members’ requirements;

(c)     Climate-related diagnostic products, particularly for tropical regions.

WMCs shall also carry out verification and intercomparison of products, support the inclusion of research results into operational models and their supporting systems, and provide training courses on the use of WMC products.

4.1.2     Regional Specialized Meteorological Centres (RSMCs)     Centres with geographical specialization

These shall be either existing national or regional centres which have accepted responsibilities by multilateral or regional agreement, or centres implemented by a joint cooperative effort by several countries in a Region. The functions of RSMCs with geographical specialization shall include:

(a)     Providing the interface between WMCs and NMCs by formatting and distributing global products to meet the needs in a particular Region;

(b)     Providing regional analysis and forecast products for 12–48 hours, for designated areas;

(c)     Providing meteorological assistance to United Nations humanitarian missions, in the event the relevant associated NMC is facing an emergency or is in catastrophic distress and out of service, as specified in Appendix I-5;

(d)     Coordinating with other RSMCs as appropriate.     Centres with activity specialization

The functions of RSMCs with activity specialization shall include, inter alia:

(a)     Providing long-, extended- and/or medium-range forecasting products;

(b)     Providing advisories for tropical cyclones, severe storms and other dangerous weather phenomena;

(c)     Providing tailored specialized products to service users in a particular area;

(d)     Providing trajectories or dispersion of pollutants in case of environmental emergencies;

(e)     Providing information on prolonged adverse weather conditions, including drought monitoring;

(f)     Undertaking activities related to the WCP and other WMO international programmes. This
includes providing climate diagnostic, climate analysis and prediction products to assist in climate monitoring.     RSMCs shall also carry out verification and intercomparison of products and arrange regional workshops and seminars on centres’ products and their use in national weather forecasting. RSMCs with geographical and activity specialization shall be co-located where possible.     RSMCs designated by WMO for the provision of atmospheric transport model products for environmental emergency response shall implement the regional and global arrangements and related procedures in Appendix I-3.     The designated WMCs and RSMCs are given in Appendix I-1 and the procedures for broadening the functions of existing RSMCs and for designating new RSMCs are given in Appendix I-2. Regional and global arrangements for the provision of transport model products for environmental emergency response are given in Appendix I-3.

NOTE: Guidelines to review the status of RSMCs with geographical specialization are given in Attachment I.1.

4.1.3     National Meteorological Centres (NMCs)

The NMCs carry out functions to meet their national and international requirements. Typically, the functions of NMCs include the preparation of:

(a)     Nowcasts and very short-range forecasts;

(b)     Short-, medium-, extended- and long-range forecasts by applying objective or subjective interpretation methods to products received from World and Regional Specialized Meteorological Centres or by integrating regional models using boundary conditions based on these products;

(c)     Special application-user products, including warnings of severe weather, climate and environmental quality monitoring and prediction products;

(d)     Specific products and their delivery in support of United Nations humanitarian missions as specified in Appendix I-5;

(e)     Non-real-time climate-related analyses and diagnosis.

NMCs should be linked via suitable terminals to computer systems at other GDPS centres in order to carry out inter-processing activities between centres, according to bilateral or multilateral agreements among Members. The definition of forecast ranges is given in Appendix I-4.     The basic organization of the GDPS is also given in Chapter A.2.1 of the Technical Regulations.


(1) The national data-processing activities may also be concerned with large-scale analyses and forecasts.

(2) Detailed specifications of the real-time and non-real-time functions of WWW centres are given in Parts II and III, respectively.

(3) Procedures for the elaboration of observational data requirements are given in Attachment I.2.

(4) In some instances, WMCs, RSMCs and NMCs are co-located and the functions of one centre are included in those of the other.

4.2     The above functions of the various centres shall not affect the status of any international commitments of Members for support to shipping and aviation, nor determine the manner in which Members execute these responsibilities.


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