During the run up to launch, I make predictions using data provided by NOAA for the actual day of the flight.
I decided for the flight of EOSS-66 to archive all of the pre-flight predictions so that folks could see just what kind of variability you might expect. Click on 13 days to launch and you can use the nav options on each page to move forward and backward between predictions.
Each page linked above has the map of the prediction, Balloon Track's data output, and the data as obtained from READY for the prediction.
If the art and science of weather prediction were perfect, then the the tracks predicted would be the same from the beginning of the process 10 days out to launch day. However, as each day passes, new data arrives at NOAA and the predicted winds aloft for launch day reflect that new information. Sometimes mother nature pays no attention to the folks at NOAA and provides data that is inconsistent with their previous models. And so, the touchdown site prediction varies.
The closer to launch the more accurate these predictions become.
One problem, if a front is expected to pass through within 24 hours of launch the prediction can change wildly from day to day right up to 48 hours or so of your flight.