8889 posts
There will most likely be stretches where you are travelling through snow and some where the snow will have melted. At that time of year it depends on altitude. Enjoy the variety.
http://www.myswissalps.com/gl acierexpress
http://www.myswissalps.com/be sttimetovisit
72625 posts
There is likely to be snow on the tops of the surrounding mountains, but by the side of the railway, the snow will have mostly melted along the Glacier Express route by May, except there could be a covering or at least quiet a few large patches left at Oberalp Pass, the highest point reached by the Glacier Express
8889 posts
There was quite a bit of snow on the Oberalp Pass when I passed that way in the last week in May 2017. That was the only bit we saw apart from on the peaks. In Brig the temperature was 29C.