Sorry…I know who WMO are and how they fit into the equation. My comment about US units issues is that the intended purpose for sharing XML files was to allow data sharing between web sites. When the subject of units comes up there is often a comment from US users that they don’t want Celcius because no-one understands it. WD is littered with tags showing degF equivalents of the base degC data (and other units) mainly to suit the US market.
I have no problem with degC…although KTS is a bit alien to me. I tend to read KTS as being more or less MPH to avoid confusion!
Have you found the NWS XML schema definition?