I've got involved in a question:
"There are many websites describing plot symbols for weather maps. Why some are different?"
Is there really difference? Yes, unfortunately.
Currently valid definition of the symbols are given in the Attachment II-4 of the Manual on GDPFS Volume I (WMO Pub No.485). The symbols are given in 10x10 table indexed by two-digit number ww, and the meaning of the numbers are defined in the code table 4677 of the Manual on Codes, Volume I.1 (WMO Pub. 306). Those are all online in PDF --- thanks to the Internet. But you can find several websites showing slightly different tables, for example http://www.australianweathernews.com/learn_about_surface_charts.htm or http://www.asahi-net.or.jp/~ns8m-hgc/w-wld1.htm . The differences are (as far as I found):
- 00-03 have circle-like symbols, which are currently absent,
- 07 does not have alternative symbol like cursive lowercase L for ocean spray,
- 11 is *two* horizontal broken bars, unlike current *three* broken bars (☷ or http://www.fileformat.info/info/unicode/char/2637/index.htm), and
- 12 is *one* broken bar over another bar, unlike current *two* broken bars over another bar (☳ or http://www.fileformat.info/info/unicode/char/2633/index.htm).
- 1962: Rec.67 CSM-III decided the symbols for 11 and 12 should be the present style. The text suggests there were confusion before that.
- 1970: ¶6.4.2.2 CSM-V introduced the symbol for spray (code 07). It also decided removal of many code points including 00-03, but those are not carried out at that time.
- 1980: Rec.7 CBS-Ext.(80) superseded the symbol table with new one in which code points 00-03 remain blank.a
The final reports of CBS (Commission for Basic Systems) and CSM (Commission for Synoptic Meteorology) are found here: http://goos.kishou.go.jp/ws/ETMC/code_task/doc_cmm_cbs.html
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