Jungfraujoch possible as a day trip ?

It makes little difference what the averages far for late April. It will depend on what the weather will be on the specific date you are looking at. And that is simply impossible. It is certainly possible to do it as a day trip, especially in Switzerland where trains are fast and frequent. You could wait until the last minute, look at the current weather and go if the conditions are favorable for good weather. Your best chance would be to go from Zurich to Interlaken or Lauterbrunnen and wait and see. There are lots of things to do and see there while you wait to see what the weather will be.

Thanks for the quick reply! Are you familiar which train or bus to take from Zurich & fares for the trains? I've seen fares for a Swiss Card(?) it would only be a one day ticket.
How far from Interlaken, by train, to Zurich...is it truly 4 hrs? TIA

It would be possible to make a day trip to the Jungfraujoch, but it would be a long day as travel time via train from either Zürich or Basel is about 2.5 hours each way (to Lauterbrunnen - extra time from there to the Jungfraujoch). The trip will be slightly easier from Basel, as there's only one change at Interlaken Ost. As the previous reply mentioned it's a good idea to check the weather, as if the top of the Jungfraujoch is shrouded in fog, you won't see much. That will be an expensive day trip, but it's a very unique site.

Travel by Bus is not a good option as those will take longer. Renting a car also won't be prudent, as you'd have to leave the car parked in Lauterbrunnen. Some of the mountain villages are car-free, so it's not possible to drive. You can check prices and other rail details on this site - https://www.sbb.ch/en/home.html

I would plan on staying at “least one night in the Lauterbrunnen valley. This is where u would start for your ride up to Jungfrau if clear. There are many other areas to see conveniently in the valley also as an option. The area FYI really warrants 3 to 4 days it is absolutely beautiful and should not be rushed imo.
A day trip from Zurich or Basel to the J peak is really not doable . It is too far for a daytrip.

Thank you, for your responses! My husband surprised me with this trip, for Anniversay #20. Unable to adjust our time in Zurich -2 days before boarding in Basel. Viking has an optional tour from Basel: Brienz>Grindelwald>Kleine Scheidegg for lunch> Grindelwald>Interlaken
This is 10 1/2 hr $300/pp. Just wondering if this would be a good tour...I understand about the weather (fog) dictating the view (I'm from San Francisco -lol).

If I could read between the lines here, sounds like you are flying SFO to Zurich, departing 4/25 on the Swiss nonstop, arriving 4/26 at 3:50 pm. So instead of staying in Zurich, go directly to Lauterbrunnen on the train from the airport. I see there is one at 4:40 pm that will get you there by 7:25 pm. Get a hotel there and sleep off the flight. If you are late arriving, there are trains at least every hour to Lauterbrunnen, the last one at 8:43 pm.

Next morning, see if the weather is good and take the earliest train to Jungfraujoch. first one is at 7:07 am and it takes about 1 1/2 hours to the top. Spend as much time as you like and come down when you want. There are trains every 1/2 hour. If the weather is not favorable, wait to the next day and try again. Otherwise, you can a return train to Basel at your leisure, they go every hour and take about 2 1/2 hours.

Trains in Switzerland are always the same price and reservations are not needed. Costs would be 82.60 CHF Zurich airport to Lauterbrunnen per person, 94.80 CHF to the Jungfraujoch per person, same for the return to Lauterbrunnen. Lauterbrunnen to Basel SBB station is 78.60 CHF per person. So tickets will be 350.80 CHF. However, you can purchase a Swiss 30-day Half Fare Card at the start for 120 CHF per person. So now the cost for the tickets will be half price. Now you will spend 120 CHF for the card and 175.40 for the tickets, so the cost is 295.40 CHF. CHF is roughly equal to the USD right now.

Bottom line, if you want to do the Jungfraujoch, this is a better plan than spending 2 nights in Zurich, which is, how shall I say, meh? If the weather is not conducive to going up to the Jungraujoch, there will be lots to do there. Visit Muerren, an iconic Swiss village on the side of the mountain, Interlaken and boat rides on the lakes. Even going up as far as Kleine Scheidegg. Maybe you'll run into your future shipmates at lunch.

But since you are arriving/departing from Zurich a much better option is to spend your time in Lucerne - only 55 minute train ride from Zurich. It's on the beautiful River Ruess and provides quick access to Mt. Pilatus.

A day trip to the Jungfraujoch is just not at all a good idea from Zurich. It's too long (4+ hours 1 way). That would be over 8 hours of just sitting on trains which is not including any time at all to actually step off the train and do/see anything along the way. And a trip to the Jungfraujoch is ALWAYS dependent upon the weather which can change in the blink of an eye. Lastly - the cost will be 350chf per person roundtrip from Zurich to the Jungfraujoch. There are so many beautiful things to see in Switzerland and spending 700chf to sit on a train for the biggest part of a day (when you only have 2 days) is just not a good idea.

If you decide to trek to the Jungfraujoch then by NO means do you need to pay a tour operator. You simply buy a ticket at any Swiss Train station (including the one in the Zurich Airport) and hop on the train.

Drilling down a bit deeper and reading your other posted questions, things are getting clearer.
You've booked the Viking River Cruise Zurich to Paris beginning with 2 nights hotel in Zurich starting April 28. Your actual cruise starts Monday April 30 from Basel going to Trier over 8 days, then a day in Luxembourg, then 2 nights in Paris.

Since your tour includes 2 nights hotel in Zurich, I can see your reluctance to spend nights away from the city. Will Viking transport your luggage to the boat in Basel without you? Then you could try your hand at the Jungfraujoch on Monday and return to Basel for about 291 CHF with the Half Fare Card. Or, on Sunday, Viatour has a day tour to the Jungfraujoch from Zurich and return for US$239. That would be a charter bus to Lauterbrunnen and train tickets up to the Jungfraujoch and back, and return to Zurich on the charter bus.
https://www.viator.com/tours/Zurich/Jungfraujoch-Top-of-Europe-Day-Trip-from-Zurich/d577-2460JUNG

For other stops on the cruise, I see there are included day trips at each stop. I see no good reason to hire private guides along the way. If a trip to Burg Eltz is not included with your stop at Cochem, we can show you how to get there on your own.

If you're flying overnight to Zurich from San Francisco a couple of days before your anniversary cruise, don't forget to allow plenty of time to recover from jet lag and sleep deprivation from that flight, or you'll feel like an exhausted zombie desperately fighting sleep in order to take in your surroundings. My thought is that the Jungfrau is too far away from Zurich to be a practical day trip when you'd be so tired. You could have a nice time in Zurich and nearby charming Lucerne, and still stay close enough to your already-locked-in Zurich hotel to get back to catch up on sleep before your cruise starts. And it's your cruise that's what your anniversary surprise was meant to be, not the alps, way down south of there. Maybe a stay in the alps would make a good future anniversary surprise?