Last year we didnt have much of a big spring storm season and they were open till May 11.
Go back to 2006, and they were open till early June right? I dont remember... but I know they got a few inches of snow that year in epic-ly late May... remember that just because i was a bit astounded. Pretty sure they reopened for 4th of july too, just because they could...
I'd say they should be open at least thru mid-late may...