What is the difference in meaning/usage between "vorhersagen" and "voraussagen" ?
Is one more commonly used than the other?
"voraussagen" is forecasting. A forecast tries to predict the future by extrapolating current data.
"vorhersagen" is foretelling. Foretelling means telling someone the future without having clear data, or otherwise having obtained information by somewhat "occult" means.
Basically the difference between "voraussagen" and "vorhersagen", is the difference between a stock market analyst and an oracle.