An Android soaring forecast app was developed to help consolidate various forecasts and information useful for soaring(aka gliding) pilots. To help with assessing soaring conditions a customized version of Windy was added via an Android webview.
No, it depends on the weather model you look at. Then it depends on the time stamp. For the next day it is quite accurate, after 5 days the accuracy drops down. And there is not a fixed probability for each model and each date. It varies with different weather factors.
Referring to the ECMWF model, this article may give you more information https://www.ecmwf.int/file/261993/download?token=yI5PPoX6
Just as example