A friend of mine just arrived at the Monchsjoch Hut, about a 1-hour hike from Jungfraujoch.
He ran into whiteout conditions. I have experienced whiteout four times myself. It’s almost a psychological nightmare.
According to Wikipedia:
"Whiteout causes the horizon to disappear; ground and sky merge seamlessly. Contours and shadows are no longer recognizable, and the observer feels as if they are in a completely empty, infinitely extended gray space. For some people, this can lead to severe psychological stress, often expressed as feelings of oppression and anxiety. Physically, whiteout causes disorientation and impairs the sense of balance."
Even on this prepared and clearly marked trail (not open all year), conditions like this become extremely dangerous. With (almost) no visibility, you can step just a few meters off the trail and suddenly you are on the glacier, where hidden crevasses may be covered by snow.
Even in perfect weather, this trail is not for casual tourists in sneakers. Proper gear and experience are essential.