A METAR decoder written in R.
Status: the decoder works up to the altimeter (or QNH) group.
An extended test suite is needed.
The description of METAR decodification is based on two manuals, there are two main METAR formats, I call them the international format and the USA format; there are differences in the two formats for example regarding the units of measure (where the international format prescribes the SI units while the USA format prescribe different units) or the abbreviations.
The international format is described in a manual from the World Meteorological Organization:
Manual on Codes International Codes Volume I.1 (Annex II to WMO Technical Regulations) Part A – Alphanumeric Codes WMO-No. 306 2011 edition Updated in 2012 ftp://ftp.wmo.int/Documents/MediaPublic/Publications/CodesManual_WMO_No_306/WMO306_Vol_I.1_2012_en.pdf (accessed 20130528)
The USA format is described in this manual:
FEDERAL COORDINATOR FOR METEOROLOGICAL SERVICES AND SUPPORTING RESEARCH 8455 COLESVILLE ROAD, SUITE 1500 SILVER SPRING, MARYLAND 20910 301-427-2002 www.ofcm.gov FEDERAL METEOROLOGICAL HANDBOOK NUMBER 1 SURFACE WEATHER OBSERVATIONS AND REPORTS FCM-H1-2005 Washington, D.C. September 2005 http://www.ofcm.gov/fmh-1/pdf/FMH1.pdf (accessed 20130529)