Teroc, thanks for that. It confirms my suspicion that the code is linked to a start or end of precipitation, but I'm still hoping that someone can confirm that it is just an incomplete section, instead of something special.
I've found this about it (from
this page):
Beginning and Ending of Precipitation (w'w'B(hh)mmE(hh)mm). At designated stations, the beginning and ending of precipitation shall be coded in the format, w'w'B(hh)mmE(hh)mm, where:
w'w' is the type of precipitation,
B denotes the beginning,
E denotes the ending, and
(hh)mm is the time of occurrence (only the minutes are required if the hour can be inferred from the report time).
There shall be no spaces between the elements. The coded remarks are not required in SPECI and should be reported in the next METAR. Intensity qualifiers shall not be coded. For example, if rain began at 0005, ended at 0030, and snow began at 0020, and ended at 0055, the remarks would be coded "RAB05E30SNB20E55". If the precipitation were showery, the remark would be coded "SHRABO5E30SHSNB20E55".
So you could have SNE05, meaning that snowing ended at 05 past the hour. I'm pretty sure that the SNEMM group is a variation on this, but did someone just forget to add the time, or is there a special meaning associated with this variation?