Switzerland early spring train trip: snow?

I have a fantasy trip in my head for next winter/spring and need input about Switzerland. Thinking of connecting a week in Venice and a visit to see tulips in Netherlands with a trip through Switzerland on the Bernina Express or similar. I love Venice in winter and early spring, and Keukenhof is often at its prime in mid April. If the world were perfect, I would like to look out the train window and see lots of snow! Please set me straight if I am delusional about how long snow lasts along this route in Switzerland. I can do some date shifting to try to make this work. Input welcome. Many thanks!