Re-opening this old topic to mention some METAR changes in 2017.
The
International Civil Aviation Organization have changed their guidance Annex 3 to the Convention on International Civil Aviation, reflecting their project to move airports from reporting METAR using Traditional Alphanumeric Characters format that only trained humans can understand to a new format designed to be proicessed by computers.
World Meteorological Office specification for METAR is in WMO Document No. 306, Manual on Codes, Volume 1, Part A; current form code FM 15–XIV - the Roman numeral XIV identifies the session of CSM (Commission for Synoptic Meteorology) or of CBS (Commission for Basic Systems) which made the latest amendment and this indicates that latest update has changed several times from the FM 15-IX that is indirectly referenced by this thread. I have not purchased any WMO document (WMO sell them, they do not make them available for free viewing on-line), but have gained an impression that WMO are trying to tighten the specification to make METAR more consistent internationally for example by standardising on units used for wind speed and cloud height and removing a few seldom used formats (WMO have withdrawn the 'VVVNDV' format (as of June 2011)) as well as working with ICAO to persaude countries to adopt the new digital format.
EDIT - ICAO/WMO in 2016 announced (http://www.ofcm.gov/groups/iwxxm/meetin ... status.pdf) that the METAR format of traditional alphanumerical characters (TAC) would be replaced by a new international XML style version mandatory from ICAO Standards and Recommended Practices - Annex 3 Amendment 78 (November 2020). The new format IWXXM is being developed by WMO and ICAO.
IWXXM Messages will be exchanged over Aeronautical Message Handling System (AMHS) as the Aeronautical Fixed Telecommunications Network (AFTN) can't accept them.
The
UK Civil Aviation Authority defines content of METAR in chapter 4 in 'CAP 746: Requirements for Meteorological Observations at Aerodromes', they published version 4 of that guidance in March 2017. The changes from 2003, 2012, and 2014 versions are listed on pages 9-11 of the document (too many to list here since the previous post in this topic) and it can be downloaded freely from "
http://publicapps.caa.co.uk/modalapplic ... il&id=1110".
The
US standard for aviation surface observations is in Federal Meteorological Handbook No. 1 (FCM-H1-2017), that is a new edition just published that will be effective 30 November 2017 found at "
http://www.ofcm.gov/publications/fmh/FMH1/FMH1_2017.pdf". Again the changes from the September 2005 edition are listed in it, they relate to snow pellets, hail, present weather, reporting timings for precipitation of all types (not just rain), intensity modifiers for precipitation, and ice accretion.
Current raw METAR (excluding NIL reports) can still be read from '//tgftp.nws.noaa.gov/data/observations/metar/stations/????.TXT' (where ???? is replaced by the relevant ICAO identifier) using either CURL, file socket reads, or FTP. Any METAR back to 1 January 2005 can be downloaded from a storage database at
http://www.ogimet.com/metars.phtml.en (with an option to output in text format) and viewed on a web page on that site.
Steve Loft published (back in January 2008) a guide to METAR content at
http://weatherfaqs.org.uk/node/197. There are a number of decoders still available online, they vary in how much of a METAR they actually turn into plain English, most focus on the mandatory groups and ignore the optional groups and those that are country specific rather than international in their usage. Several Cumulus-using web sites already include Ken True's script available at "
http://saratoga-weather.org/scripts.php" rather than the Nirsoft programme mentioned in this topic, there you can either download a stand-alone zip that contains scripts for reading METAR, for decoding them including a web page that displays them, or you can download his whole package that displays information from many sources (more information in Saratoga Templates part of forum).
If anyone is interested, I have written in PHP a METAR decoding script suite that takes into account all the 2017 changes listed above. Although initially based on the guidance in the 'CAP 746' document, because I first used it for decoding UK METAR, I have extended it to world-wide coverage. [EDIT - corrected spelling errors in this paragraph].
Although I believe my script will work in other environments, it was written to run on my PC's web server (from Uniform) in conjunction with other scripts that I have on my server, my decoder script does not include any language translation options, it simply takes in a raw METAR string (a separate script is needed to read the METAR from the sources I mention), and populates an output array (a separate script is needed to take information out of the array and produce a web page). I cannot commit to support, so you need some expertise in PHP to do any tailoring you want. My script is well commented, it has optional diagnostic output to show what it is doing as it decodes a METAR and it will output the whole METAR to a text file if it finds it cannot decode part of the content. I have used this last feature to rewrite my code to cope with more extensive METAR decoding (unfortunately some aerodrome observers do make coding mistakes sometimes, and some countries effectively allow free text).