This decode is actually to do with temperatures. If I remember correctly it translates as "the maximum temperature will occur at 21h00 and will be 6degC".
I think that the format of the second part of the message should be TN01/06Z, meaning "the minimum temperature will occur at 06h00 and will be 1degC".
If this isn't correct, it is probably not that far out. I have been looking for a reference for this type of TAF information for a while, but have not been able to find one. If anyone has a source, please let us know.
G W-H