Whether it is advisable to purchase mountain excursion tickets in advance is frequently inquired.
I say, it is not recommended to purchase mountain excursion tickets too far in advance. The weather in Switzerland, particularly in the mountains, can be unpredictable, especially for more than two days. The weather conditions on mountain peaks can range from sunny and blue skies to stormy with rain or snowfall. September is usually a great time for Switzerland and mountain visits. On a sunny day, visibility is much better in autumn compared to the summer because in autumn, there is less humidity in the air, which results in better sights.
Furthermore, the Jungfraujoch, along with other mountain peaks such as Mt. Schilthorn or Mt. Titlis, are deemed as costly excursions. Buying tickets in advance will mean that you will spend money in advance and might end up in the clouds, with no vistas. As a local, I suggest delaying the purchase of tickets until you’re in the area, and you know the weather forecast. Unless you decide to visit the places no matter the actual weather.
You can reserve seats for the Jungfraujoch trip on this website: Book Priority Boarding | jungfrau.ch