I was at Europa-Park over the New Year and it was quite astounding just how they managed to get rollercoasters open...
30th December AM - heavy snow and only Eurosat was operating. However, by late afternoon both Pegasus and Matterhorn Blitz opened.
31st December - Euro-Mir had technicians on the track working at 90' with brushes - snow was falling off several of the MCBRs. The ride opened around 1pm. Arthur also opened shortly after and so did Alpenexpress.
1st January - Same line up as 31st - although temperatures peaked at around 0C and were negative Celsius for a lot of the day.
2nd January - somehow, even with the cold and snow remaining around the park, Wodan opened early in the afternoon!
Most parks just wouldn't have bothered even TRYING to get coasters operating in freezing and snowy conditions! The vast majority of other rides were open as expected.