The answer to your question is difficult, as only WRI can tell you what exactly is wrong when these functions don't work. If you are using a desktop Mathematica version I don't think that Wolfram Credits are even needed to run
WeatherData or any of the data functions, so I would exclude that as the reason for the problems you have been seeing. Unfortunately as the functionality depends on interaction between your local installation and some services provided by WRI there are plenty possible reasons for such problems.
There could be a problem with their servers, but if you encounter networking problems that would also explain why you can't get data. There have also been reported cases where the data paclet infrastructure of individual installations has been broken. You can find other questions on this site which explain how one can clean up and reset those.
As several users have reported the same problem during the same time period I would guess that this time it has been a (temporary) problem on the server side. It now (about 24h after the first failures) seems to have been repaired. Unfortunately the information we get when errors occure and other possibilities to get information about the server states are quite limited, so we are left with hoping and speculating...