First, a Skew-T log (p) diagram is a thermodynamic chart. It has nothing to do with rawinsondes (weather balloons) that get launched routinely twice a day. The data from the rawinsonde flight is called a rawinsonde observation or RAOB. RAOB data can be plotted on a thermodynamic chart such as the Skew-T log (p) diagram, Stuve diagram or Tephigram (all are thermodynamic charts).
Also, pressure, temperature, dewpoint and wind data from forecast models such as the Rapid Update Cycle (RUC), North American Mesoscale (NAM) or Global Forecast System (GFS) can also be plotted on the same thermodynamic charts.
The advantage of using the RUC model data is that its temporal and spatial resolution are much better than you can get with the FBWinds. If you want to use low resolution data from a DUATS or FSS briefing, that's fine. Just understand that there are some gotchas as I discuss in
this free workshop.
I hope this helps.