Synop decoder software into tabular/plain language?

Hi everyone,

I am looking for a plain language synop decoder.
Gempak is nice for standard meteorological values, but the weather,
cloud coverage, cloud base, cloud types, are being reported in codes.

Is there available some (free) software that would run on unix that
would convert a raw synop report (with possibly regional code section)
in tabular data (or plain language) for all parameters?

Many thanks,
--
Christian Pagé
UQAM