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These pages document the various XML schemas used to encode products that originate in the United States (US). These schemas fall into two general categories, schemas governed by the US exclusively and extensions to schemas governed by other Standards Development Organizations (SDO). 

Weather Schema Extensions


IWXXM-US was originally developed to support the XML encoding of four Traditional Alphanumeric Codes (TAC)--METAR, SPECI, TAF, and SIGMET for use within the US. IWXXM-US is an extension to the IWXXM within AvXML. (See below.)

Two principles guided the development of IWXXM-US. First, IWXXM-US needed to support all filed differences maintained by the US for METAR, SPECI, TAF, and SIGMET. Second, IWXXM-US should enable the development of straightforward techniques that convert products from US-specific formats to formats that comply with international standards.

The World Meteorological Organization (WMO) and the International Civil Aviation Organization (ICAO) have jointly developed an XML package named AvXML, that can represent meteorological information that is compatible with both WMO and aviation systems. AvXML is comprised of four packages named METCE, OPM, IWXXM, and SAF. Documentation for AvXML and all four packages is available at

Since the initial release of METAR, TAF and SIGMET schemas, new XML products based on TAC have been added to IWXXM-US namespace. Please go to the Product and Schema page for a list.


Schemas and documentation for the latest version of IWXXM-US are hosted on these pages at


MDL's Role in Data Modelling



Weather Schemas Governed by the United States


The USWX was developed to support XML encoding of meteorological products issued by the United States that are not found in ICAO Annex 3 product suite. Schemas and documentation for USWX products are hosted on these page. Please note that the US AMDAR schema and example will be superceded by WMO in the near future as they have goverance on the AMDAR program.