IWXXM - The "ICAO Weather Exchange Model"

Historical Background

The development of IWXXM, although it was no called like that, started approximately in the year 2004. The main reason was the plan of WMO (World Meteorological Organization) to replace all alphanumeric code forms by a binary, table driven code form BUFR (Binary Universal Form for the Representation of meteorological data). Information on BUFR can be found in the WMO Doc. 306, Volume I.2 (Manual on Codes). On the WMO-website you can also find "A Guide To The Code Form FM-94 BUFR".

The WMO governs also the meteorological TAC-codes used by ICAO (METAR, SPECI, TAF, AMDAR) and therefor the intention was to replace those as well. At the EANPG/46 (2004) first conclusions were defined in order to analyse the impact of such a transition. Many concerns were raised during that process from regional planning and implementation groups. The discussion led finally to the decision not to use BUFR but develop an XML(eXtensible Mark-up Language) representation for ICAO weather data.

In 2009 the WMO completed a pilot project to demonstrate the feasibility of sending XML-coded OPMET data via AFTN. After that, the development of AvXML (Aviation XML) started, involving experts from WMO, ICAO as well as Eurocontrol.

In 2010 also the DMG got involved with the task, defined by METG/20, to analyse the implications of the ongoing developments.

The term AvXML was replaced by IWXXM (ICAO Weather Exchange Model). The first release candidate (RC) for IWXXM 1.0 was provided in December 2012. After receiving back several problem reports, this RC was reworked leading to a second RC, which was issued in May 2013. Finally, in September 2013 IWXXM 1.0 was officially released. But it took nearly two years, until June 2015, to have it approved by WMO as IWXXM 1.1.

In September 2015 the 17th WMO World Congress agreed to add a new, third Volume to the WMO 306 (Manual on Codes) ==> Volume I.3, Part D – Representations derived from data models.

Unfortunately, the first version of IWXXM, although reworked after review by users, still contained a lot of issues and therefore a majority of states decided to not implement but wait for the next version. The RC for IWXXM 2.0 was issued in April 2016. After it was reviewed, the version IWXXM 2.0, again with a number of changes based of feedback by users, was provided in August 2016, which was approved and released by WMO as version IWXXM 2.1 in March 2017.

IWXXM 2.1 - First Operational Usage

Short after the release of IWXXM 2.1, Belgium started to produce METAR and TAF in IWXXM-format (July 2017). France followed in October and Austria in November the same year. In the meanwhile, the DMG also developed the document EUR Doc 033 "Guidelines for the Implementation of OPMET Data Exchange using IWXXM in the EUR-Region". This document explains the differences of the operational principles when exchanging TAC- and/or IWXXM-data. It also gives guidance on translating TAC to IWXXM. This could be done nationally by a state or by the responsible ROC. For the latter the DMG developed a Translation Agreement.

Supporting the Transition to use IWXXM

Since November 2020 (according to ANNEX 3, Amendment 78) all OPMET-data shall be provided in IWXXM-format, in parallel to the produced TAC-data. Some states might not be in the position to cope with that requirement. For this purpose, a special service is offered to NOCs within the EUR-region, who can request a translation service from their responsible ROC. A "TAC to IWXXM translation service request form" can be found on the ICAO Paris website. Several states are using this service.

This service is not meant to be infinite. It will be reviewed on a yearly basis by METG (meeting in September) whether the service will be continued or cancelled. States are therefore highly encouraged to implement either IWXXM-production at source or a install a translation function e.g. at the national MET-switch.

IWXXM 2.1.1

The sub-release of IWXXM 2.1 corrected some issues of IWXXM 2.1, especially in regard to schematron rules. A graphical representation of the IWXXM 2.1 schema can be found online.

IWXXM 3.0

The first Release Candidate for IWXXM 3.0 was provided in July 2018, followed by 3 more release candidates, which fixed identified issues. The new version includes several improvements, especially for the generation of SIGMET/AIRMET-messages. New to the schema is the possibility to code Space Weather Advisories. For METAR/SPECI all elements have been changed to be nillable. This was identified to be necessary for automated stations, which may not report some parameters because of non-detection or a broken sensor. It also supports the possibility to add national information to the existing schemas. The United States already took advantage of this. You can find details on the website of the NOAA MDL(The Meteorological Development Laboratory).

Detailed information about all changes so far can be found in the release notes on the GITHUB-website.

IWXXM 3.0 was officially released on 7. November 2019 and has to be applied since 4. November 2020. A graphical representation of the IWXXM 3.1 schema can be found online.

Current Status and Future Developments

At DMG/35 (March 2022) the latest news have been presented on the current developments. Please feel free to have a look at the Power Point presentation. One very important and interesting information is, that the way of versioning new IWXXM-schemas was changed. Detailed information can be found on the GitHub.

If you have special questions about the IWXXM-code you can contact the IWXXM-development team (TT-AvXML). Of course you may also contact your responsible ROC-representative or ICAO EUR/NAT Headquarters in Paris who will try to answer your questions.