I think lausanne and gstaad are closest ones to interlaken... be a good 2 odd hours away though..
Best bet is to the check the resort sites, they will have the info up - some even tell you which jumps/rails are up.
I'm pretty sure that if theres snow, the park at saas fee may be already open - not sure though.
If it doesnt say on the site if the parks open, just email them and they usually respond within a day.
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